Update redhat updates test - updating from multiple versions

Removed original test

Updated yaml template

Added separate update tests

Update utils/appliance.py:
  Add migrate_db method
  Loosen_pgssl doesnt run on non-DB appliances anymore
  _custom_configure method extended to be able to use all available post-deployment methods

Increase appliance registration timeout

Stream excluder runs first

Dont test Sat6 - added BZ mark

Add ssh.run_in_background()

Add rh_updates mark

Prettify and refactor

Primary must be first in ApplianceSet.all_appliances