qa_crowbarsetup: Always setup SLE12 repositories for Cloud 5+

This allows e.g. the QA team to manually go in and install more than
one SLE12 node.
qa_crowbarsetup.sh: Don't modify DNS proposal before node allocation
qa_crowbarsetup.sh: Stop creating DNS proposals

The DNS propsal always exists, we just need to update it instead
of trying to create a new one.