AURORA-543: Resources should be an allowed dependency of python libraries within src/main/python.

Testing Done:

./pants src/main/python/apache/thermos/observer/bin:thermos_observer && \
 unzip -l dist/thermos_observer.pex to validate contents with .tpl files.

Bugs closed: AURORA-543

Reviewed at https://reviews.apache.org/r/22894/