Integrated customizable bash prompt

Get a nice configurable shell prompt for all nodes... YEAH!
This is a followup pull request after discussion on https://github.com/crowbar/barclamp-deployer/pull/219
@tboerger it's good that it was done in a separate commit, and I have nothing against the other bits of the reformatting. But this one change about escaping / is going, I think, to hit us at some point, either as an inconvenience, or when it will create some misunderstanding.