[build] Use python_binary in mesa template

... for mesa_python_stdout_to_file_action

This allows us to set python libraries as dependencies, instead of
adding their sources as inputs directly.

python_binary requires scripts to have a main function, so a few
scripts are updated for this.

Change-Id: I49ae526befb79f38bcf441b4449406f13560321a
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/516200
Reviewed-by: John Rosasco <rosasco@google.com>
Reviewed-by: Shai Barack <shayba@google.com>
12 files changed