Prefer qemu-system-x86_64 if available

Otherwise on openSUSE 13.2 starting the admin domain fails
due to missing cpu capabilities (since the qemu-kvm binary
is not evaluated correctly by libvirt)
Merge pull request #137 from dirkmueller/master

Prefer qemu-system-x86_64 if available
mkcloud: Test the packaged state of crowbar-backup

The script fetched some random git state from master instead of
testing what was actually packaged. It makes more sense to gate
on the code we ship rather than the code that is somewhere in git.
mkcloud: Install crowbar-backup again for restore
Revert workaround for bnc#900112, which is fixed
Add test for multi DNS, bnc#901497