Fix circular dependency between module_build_service.__init__ and module_build_service.backports.
This fixes issues with calling 'python module_build_service/manage.py' directly
from the MBS git repo as part of testing local module builds without installing
The issue is that 'import pkg_resources' for some reason tries to load
module_build_service.backports before the module_build_service.app actually
exists. This results in traceback saying that module_build_service.app does
This commit fixes this by importing whole module_build_service in backports.py.