RPM Support

At the moment RPM plugin relies on the rpms to be present on a filesystem.
It should be able to publish using metadata files available (primary, other, filelists).

Feb 12 20:21:54 pulp3 rq[13954]: pulp: rq.worker:ERROR: AttributeError: 'NoneType' object has no attribute 'file'
Feb 12 20:21:54 pulp3 rq[13954]: Traceback (most recent call last):
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/worker.py", line 799, in perform_job
Feb 12 20:21:54 pulp3 rq[13954]:     rv = job.perform()
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/job.py", line 600, in perform
Feb 12 20:21:54 pulp3 rq[13954]:     self._result = self._execute()
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/job.py", line 606, in _execute
Feb 12 20:21:54 pulp3 rq[13954]:     return self.func(*self.args, **self.kwargs)
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/devel/pulp_rpm/pulp_rpm/app/tasks/publishing.py", line 132, in publish
Feb 12 20:21:54 pulp3 rq[13954]:     pkg = cr.package_from_rpm(artifact.content_artifact.artifact.file.path)
Feb 12 20:21:54 pulp3 rq[13954]: AttributeError: 'NoneType' object has no attribute 'file'
Feb 12 20:21:54 pulp3 rq[13954]: Traceback (most recent call last):
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/worker.py", line 799, in perform_job
Feb 12 20:21:54 pulp3 rq[13954]:     rv = job.perform()
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/job.py", line 600, in perform
Feb 12 20:21:54 pulp3 rq[13954]:     self._result = self._execute()
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/.virtualenvs/pulp/lib64/python3.6/site-packages/rq/job.py", line 606, in _execute
Feb 12 20:21:54 pulp3 rq[13954]:     return self.func(*self.args, **self.kwargs)
Feb 12 20:21:54 pulp3 rq[13954]:   File "/home/vagrant/devel/pulp_rpm/pulp_rpm/app/tasks/publishing.py", line 132, in publish
Feb 12 20:21:54 pulp3 rq[13954]:     pkg = cr.package_from_rpm(artifact.content_artifact.artifact.file.path)
Feb 12 20:21:54 pulp3 rq[13954]: AttributeError: 'NoneType' object has no attribute 'file'