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
Not in my dev setup that was installed with mkcloud and cloudsource=susecloud3. Can we expect every deployed and updated Cloud setup to have the pacemaker barclamp installed?