Fail Azure CI for failing tests
- [x] closes #23453
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This should hopefully return a failed status on Azure
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23454?src=pr&el=h1) Report
> Merging [#23454](https://codecov.io/gh/pandas-dev/pandas/pull/23454?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cf4c0b6164506043c551e95f0036de3ee3eaf2df?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23454/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23454?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23454   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files         161      161           
  Lines       51200    51200           
=======================================
  Hits        47232    47232           
  Misses       3968     3968
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.63% <ø> (ø)` | :arrow_up: |
| #single | `42.29% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23454?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/23454?src=pr&el=footer). Last update [cf4c0b6...951f3fc](https://codecov.io/gh/pandas-dev/pandas/pull/23454?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=2227&view=logs

~~Good news the build fails on test failures now :)~~

~~I shall add this to windows/linux yml configs and attempt to de-duplicate the logic in the powershell script.~~ 

Done - please see latest comment Hello @alimcmaster1! Thanks for updating the PR.

 - There are no PEP8 issues in the file [`pandas/tests/indexing/test_indexing.py`](https://github.com/alimcmaster1/pandas/blob/e91c84efd7060938fe99d1685ca687393b9b4feb/pandas/tests/indexing/test_indexing.py) !



##### Comment last updated on November 04, 2018 at 13:46 Hours UTC This now looks like what we want:

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=2409&view=logs

Build status goes to failed on everything but ( "Linux py36_locale_slow" - which doesn't seem to run my failing test in `test_indexing.py` )

@TomAugspurger - I will now remove my dummy failing test. Any feedback/concerns with this PR?

CC: Azure Folks @vtbassmatt, @DavidStaheli - for any comments - as this touches a few files that #23111 does Sorry for the delay. This LGTM. Will merge on green.
 > Build status goes to failed on everything but ( "Linux py36_locale_slow" - which doesn't seem to run my failing test in test_indexing.py )


that's due to the `-m only-slow` marker, which skips tests not marked as slow. Ahh merge conflict :) I'll fix that up quick. Np at all @TomAugspurger my fault - I only just pushed the change to remove my failing test.  And aah thanks for the info re the `-m only-slow` marker Merged master and canceled the previous commit's build. Thanks for working on this @alimcmaster1!