CI: Format isort output for azure
- [x] closes #27179
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Current behaviour on master of isort formatting:
![image](https://user-images.githubusercontent.com/16733618/69010035-12c41f80-0953-11ea-8e70-4d17e8dec943.png)


Finishing up stale PR @https://github.com/pandas-dev/pandas/pull/27334
