Add 'no_mirror' option to controller module

The option allows to instruct the controller module to not use a mirror host
even if the base configuration has one. This allows for using a mirror host
for SLES based server and minions without the need to sync Leap repositories
for the controller.

tag before merging backend independent refactoring

More test suite advanced options

README: clarify AWS status

Use new Uyuni POOL repositories

This is the last sumaform capable of deploying a 3.1 SUSE Manager server