RPM Support

without <data type="updateinfo"> in repomd.xml in repository sync task will fail as we are checking updateinfo url which is not set up : https://github.com/pulp/pulp_rpm/blob/master/pulp_rpm/app/tasks/synchronizing.py#L299

We should change the way of how we checking record type when sync or use 'null' values to skip conditionals.

"description": "local variable 'updateinfo_url' referenced before assignment",
"traceback": "  File \"/usr/local/lib/pulp/lib64/python3.7/site-packages/rq/worker.py\", line 822, in perform_job\n    rv = job.perform()\n  File \"/usr/local/lib/pulp/lib64/python3.7/site-packages/rq/job.py\", line 605, in perform\n    self._result = self._execute()\n  File \"/usr/local/lib/pulp/lib64/python3.7/site-packages/rq/job.py\", line 611, in _execute\n    return self.func(*self.args, **self.kwargs)\n  File \"/home/vagrant/devel/pulp_rpm/pulp_rpm/app/tasks/synchronizing.py\", line 73, in synchronize\n    dv.create()\n  File \"/home/vagrant/devel/pulpcore-plugin/pulpcore/plugin/stages/declarative_version.py\", line 169, in create\n    loop.run_until_complete(pipeline)\n  File \"/usr/lib64/python3.7/asyncio/base_events.py\", line 568, in run_until_complete\n    return future.result()\n  File \"/home/vagrant/devel/pulpcore-plugin/pulpcore/plugin/stages/api.py\", line 209, in create_pipeline\n    await asyncio.gather(*futures)\n  File \"/home/vagrant/devel/pulpcore-plugin/pulpcore/plugin/stages/api.py\", line 43, in __call__\n    await self.run()\n  File \"/home/vagrant/devel/pulp_rpm/pulp_rpm/app/tasks/synchronizing.py\", line 308, in run\n    elif results[0].url == updateinfo_url:\n"