Translate _ from pacemaker proposal name to - in hostnames

The proposal names can only have letters or an underscore in their name.

A hostname cannot have an underscore in its name, but can have a dash.

As we build a virtual hostname based on the proposal name, we simply
translate the underscore to a dash so we're valid.
Merge pull request #35 from vuntz/no-underscore-hostname

Translate _ from pacemaker proposal name to - in hostnames