Fixed switch name if it is available
Merge pull request #962 from tboerger/feature/switch-fix

[roxy] Fixed switch name if it is available
Split shared code to helper function
Handle clusters in core of crowbar

It's debatable whether all this code should live here or not (as opposed
to in barclamp-pacemaker), but we do need this code to have crowbar
understand clusters.

We also provide some helpers to help barclamp authors make use of
clusters.
Integrated cluster selection into node selector
Add helpers to get hostnames for OpenStack endpoints

This is common code that all barclamps need, so a helper is a good
thing.