Add CLOUD_VERSION env var

Allows to switch between Cloud releases (currently either 2.0 or 3).
Add Devel:Cloud:Shared:11-SP3.repo

IBS repo layout changed recently. Set some priorities to make sure
Devel:Cloud projects overrule SLE repos and install media.
Configurable path for mirrored media

Control freaks mirror media to various directories (like /srv/nfs/media)
and want to expose that to VM guests.
Merge pull request #24 from saschpe/master-cloud3

saschpe-readiness (™)