No test coverage for verifying installers pull in dependencies correctly

[sbethur]

Description of issue

Unit tests run against source files of the module in generated folder. System tests are run by building a sdist, which doesn't install the dependencies. This means we don't have test coverage for verifying that the installers pull in dependencies like nitclk, hightime, etc. correctly.

[ni-jfitzger]

It looks like tox-wheel is the way to do this. It's an external plugin.

It was decided to implement support externally, before trying to add the functionality to tox core. See https://github.com/tox-dev/tox/issues/850