Adjust scripts to upgrade to Cloud 4

* Handle possible absence of barclamp-pacemaker on a non-HA setup
* Write helper-neutron-migration to do the database migrations for neutron
* Rename reboot-node to prepare-and-reboot-nodes and extend it
Hrm, I don't understand: after having applied all the Cloud 3 updates, the pacemaker barclamp should be installed. Do you mean that it wasn't installed?