Enforce py3 wheels only in CI

[scbedd]

@lmazuel This is the "hard" break on py27.

It extends the verifywhl tox environment to do the additional following checks.

1. If no python_requires is present on your setup.py, it will error.
2. If a python_requires is defined, and is not >= 3.0, it will error.
3. If a python_requires is defined and set at something >= 3.0, but a setup.cfg is still present with a universal=1 config key, it will error.

All of the above are skippable by environment variable IGNORE_WHEEL_PYVERSION_CHECK.

We can merge this PR whenever we want this to start hard erroring on py2 packages. Once that's clean, I can easily submit a PR to remove py2.7 from the build matrix.

[scbedd]

This PR will probably be green, but we should not merge immediately until we're ready for errrors to start popping up.

This PR will be green because verifywhl is not run as part of the PR suite. (that would be whl, sdist, mindependency.)

[scbedd]

Just a reminder. This PR should only be merged when we are ready to flip py3only enforcement on. This PR is currently red due to a failure to verify the wheel of various packages in core/.

Once those are fixed, a requeued check should come back green.

[ghost]

Hi @scbedd. Thank you for your interest in helping to improve the Azure SDK experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment. Otherwise, we'll close this out in 7 days.

[ghost]

Hi @scbedd. Thank you for your contribution. Since there hasn't been recent engagement, we're going to close this out. Feel free to respond with a comment containing "/reopen" if you'd like to continue working on these changes. Please be sure to use the command to reopen or remove the "no-recent-activity" label; otherwise, this is likely to be closed again with the next cleanup pass.