Comment 7 for bug 1612556

We're testing a bit different pinning schema:

* set pin-priority == 550 for all packages with origin=Mirantis
* set pin-priority == 499 for all python packages with origin=Mirantis

This should satisfy all requirements:
* to not install our python packages
* to install any package (except python-*) from our repo if
  - package not exists at all
  - package exists only in Xenial (not UCA) repositories

Using that schema there is no need to pin rabbitmq, haproxy, and so on, because they will be pinned from repo pin-priority.