TST: Test reindex w/ multiindex df (GH21247)

[calvh]

• closes reindex() inconsistency between Index and MultiIndex #21247
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

Whats new:
Add a test to pandas/tests/indexes/multi/test_reindex.py

[calvh]

Hello @mroeschke this is my first PR to the main code base.

The CI failed because of a timeout:

##[error]The job running on agent Azure Pipelines 2 ran longer than the maximum time of 60 minutes. For more information, see https://go.microsoft.com/fwlink/?linkid=2077134

I'm not sure what I should be doing to fix this issue. Is there a standard procedure?

Thanks.

[mroeschke]

Thanks LGTM. That Azure job timeout is unrelated to this test.

[jreback]

thanks @calvh