Testing and development dependencies should be available on defaults

[goanpeca]

anaconda-project testing suite currently relies on a few packages that we install via conda. We should be able to provide the necessary packages used in testing as part of the defaults channel. It would allow testing to be simplified

These packages are

• [ ] pep257
• [ ] yapf==0.6.2 We depend on this minimum version!
• [ ] flake8==2.6.2 We depend on this minimum version!

Ideally we should update the code to make use of the latest

• [ ] yapf
• [ ] flake8
• [ ] pydocstyle (which replaced the now deprecated pep257)

Thoughts @fpliger ?

[mcg1969]

2019/01/06 update:

• pep257: currently unpinned, only available on conda-forge.
• flake8: currently unpinned, available on defaults.
• yapf is now pinned to 0.25.0, and it is available and defaults.

So to close this out we only need pep257 added to defaults.