Nightly python builds

[jhamon]

Problem

We need a way to consume unreleased changes for integration testing purposes.

Solution

Publish each night, if there are new changes, using the package name python-client-nightly. This follows the practice of other large projects such as tensorflow which publishes nightlies under the tf-nightly name. PyPI does have some limited support for prereleases but releasing a lot of them under our normal package name will make the release history page on pypi look quite cluttered.

Type of Change

• Infrastructure change (CI configs, etc)

Test Plan

I successfully used this to publish to testpypi. Just changed a few variables to point at the public index.

[micmmakarov]

Looks good - just the commented out tests