Add a pyinstaller hook and simple test

[sirosen]

closes #384

This adds a pyinstaller hook and a simple test to the testsuite which tries to do a pyinstaller build of a miniscule (two line) app.

The pyinstaller hook is quite simple -- it just ensures that non-python files are included in the SDK package. The hook itself needs a setuptools entry point which identifies the hook location (one of the only bits of setuptools config pyinstaller respects).

In order for the testing to work, a few steps are needed:

• add pyinstaller to 'development' requirements for py3+
• add the test to the testsuite
• skip the test if the environment doesn't support a pyinstaller build

Skipping in the right contexts is the trickiest part. It seems that pyinstaller needs a shared-library python build. That's the default for a lot of system packaging, but it's not guaranteed. Furthermore, pyenv builds won't include shared libraries by default, but will use static linking instead. Precisely because this is so finicky, we want to allow tests without it. That way, developer laptop testing can work even if the python env isn't "just so".

GitHub Actions should build pythons appropriately to run the pyinstaller test, so we have a good guarantee of things working.

We don't test the pyinstaller hook for py2 -- if it doesn't work for that version, that's fine (wontfix).

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The one thing I wasn't sure about was where to put internal doc on this subject. Basically, I've imitated the sample repo from pyinstaller ( https://github.com/pyinstaller/hooksample ) and tried not to think too hard about this. But if we need more internal doc, maybe I could add globus_sdk/_pyinstaller/README? I'm just not certain it's necessary.

[jaswilli]

Without having any experience with pyinstaller this all seems pretty reasonable.

I can:

• Produce a broken pyinstaller bundle by using the sdk as a dependency in a test script
• See that I can build a working bundle by swapping in this branch.

Good enough for me.