Adjust scripts to upgrade to Cloud 4

Adjust scripts to upgrade to Cloud 4
* Include update-status check depending on pacemaker being present
* Write helper-neutron-migration to do the database migrations for neutron
* Extend reboot-nodes to include a mandatory migration step for neutron
* Stop chef-client on the crowbar node at the start of the upgrade process
  and restart it at the end to prevent a zypper lock.
* Extend get_allocated_nodes functionality
Hrm. Can't we just re-use `$allocated_nodes` to find out if the node is valid? The calls to `test_is_valid_node` are slow (because it does a request to crowbar), so if we can do them only once, it's better :-)