Add _expand_user to _stringify_path as we need to allow tilde - ~, to expand to full path

- [x] closes #23473 
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @srinivasreddy! Thanks for updating the PR.





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

##### Comment last updated on January 05, 2019 at 18:39 Hours UTC we have some tests in io/test_common.py ; do these need to be expanded? Nope. I do not see the need. build pass should make it good to go.  ok, can you add a whatsnew note # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23769?src=pr&el=h1) Report
> Merging [#23769](https://codecov.io/gh/pandas-dev/pandas/pull/23769?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4b4bf723e19325039bd0ce5f61bc2b8ad0651909?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23769/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23769?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23769      +/-   ##
==========================================
+ Coverage   92.37%   92.37%   +<.01%     
==========================================
  Files         166      166              
  Lines       52379    52379              
==========================================
+ Hits        48386    48387       +1     
+ Misses       3993     3992       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `43.01% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23769?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/23769/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NvbW1vbi5weQ==) | `72.86% <100%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/23769/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88.09% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23769?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/23769?src=pr&el=footer). Last update [4b4bf72...0a660e0](https://codecov.io/gh/pandas-dev/pandas/pull/23769?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 can you merge master and address comments can you merge master @pandas-dev/pandas-core if someone can merge master and update the test Sure I'll take a look @jreback all green let me know your thoughts thanks @srinivasreddy & @WillAyd 