Drop legacy kombu-requirement.patch

Fixes: bug #1194488
Change-Id: I7ce7667187cb47c0d5b36c6d550a5eee04a84a6b
Do not download Python packages again

Maintain a file indicating that all downloads are finished
and ensure that all requirements are satisfied.

Implements: blueprint pip-download-once
Change-Id: I0ddd39885d195da9a59bef2453be63990a784d32
bootstrap: install requirements before removing conflicts

Change-Id: I239601417f9b7b5fb50bad05a0ee2ee279e6596b