Add LWRP in crowbar-pacemaker to ease the creation of drbd devices

What's tricky here is that we expect the resources to be defined (as
attributes to the nodes) after the recipe will have been compiled.

That means two things:

 - users of crowbar_pacemaker_drbd will need to run the create action in
   the compile phase

 - we need a hacky LWRP to actually do the actions in crowbar-pacemaker
   in the execute phase. This is the
   crowbar_pacemaker_drbd_create_internal LWRP.
drbd: Update examples for non-crowbar usage