Python script import cleanup

[joeyparrish]

We have a few problematic patterns in our build system. Although it all works as expected in context of the Shaka Player repo, we have private infrastructure tools that import these scripts, and in that context, things are messier. In particular, we are transitioning those tools to Python 3, which changed some import semantics.

The main issue seems to be local script names which conflict with module names:

• "build.py" vs our "build" folder
• "test.py" vs "test" module (python2 & python3)
• "compiler.py" vs "compiler" module (python2 only)

I'm not sure if I've completely analyzed this, or what the best solution would be. Renaming things will create compatibility issues when using our tools during a git bisect.