BUG: Fix unexpected sort in groupby
- [x] closes #17537
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=h1) Report
> Merging [#17621](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8276a420a36c26eaab38856177023cb064963f19?src=pr&el=desc) will **decrease** coverage by `0.03%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17621/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17621      +/-   ##
==========================================
- Coverage    91.2%   91.16%   -0.04%     
==========================================
  Files         163      163              
  Lines       49637    49643       +6     
==========================================
- Hits        45269    45259      -10     
- Misses       4368     4384      +16
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.95% <100%> (-0.02%)` | :arrow_down: |
| #single | `40.18% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `92.24% <100%> (+0.02%)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.98% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `96.39% <0%> (-0.51%)` | :arrow_down: |
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `98.26% <0%> (-0.29%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=footer). Last update [8276a42...1e13713](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=h1) Report
> Merging [#17621](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ad7d051bdfdbadc4221307d691fd55412d9d7ae8?src=pr&el=desc) will **decrease** coverage by `0.05%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17621/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17621      +/-   ##
==========================================
- Coverage   91.27%   91.21%   -0.06%     
==========================================
  Files         163      163              
  Lines       49765    49770       +5     
==========================================
- Hits        45421    45399      -22     
- Misses       4344     4371      +27
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.01% <100%> (-0.04%)` | :arrow_down: |
| #single | `40.32% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `92.07% <100%> (ø)` | :arrow_up: |
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `92.25% <100%> (+0.01%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.38% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `96.39% <0%> (-0.51%)` | :arrow_down: |
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `97.46% <0%> (-0.29%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.73% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.34% <0%> (+0.05%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=footer). Last update [ad7d051...9b6a3da](https://codecov.io/gh/pandas-dev/pandas/pull/17621?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @Licht-T! Thanks for updating the PR.











Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on September 29, 2017 at 11:42 Hours UTC @jreback Thanks for your review.
- Changed the location of the solution to improve readability
- Parameterized `sort` parameter of `groupby` in tests @jreback Thank you for comments. Fixed. @TomAugspurger Okay. I'll do that. can you rebase @jreback Rebased. @Licht-T can you rebase and push once again, want to get all green here. @jreback Now all green! thanks @Licht-T 