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
It's indeed a strict requirement.

Might be worth adding a simple check like:
```
if ! rpm -q crowbar-barclamp-pacemaker 2> /dev/null; then
  echo "Please install all the latest updates."
  exit $some-return-value-that-makes-sense-likely-1
fi
```