Simplified/fixed UEFI config (bnc#865871)

I have simplified the UEFI configuration in order to get the
installation on UEFI hardware running. I extracted the UEFI informations
into an ohai plugin. This fixes
https://bugzilla.novell.com/show_bug.cgi?id=865871
Merge pull request #216 from tboerger/feature/uefi-fix

Simplified/fixed UEFI config (bnc#865871)