Pre-compile plugin Python files so they don't get stripped

Previously, the Python files were defined as _SCRIPT in automake.
Make them into _PYTHON so they automatically get compiled, and add
the compiled files to the RPMs so image-minimizer will leave
working plugins.

Change-Id: I390ca19b1abe29f19c508a9d4a41c4221d796b30
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=988484
Signed-off-by: Ryan Barry <rbarry@redhat.com>