Make live migrations work for non volume-backed instances with RBD

* Add a new ceph user and pool for ephemeral storage
* Update nova configuration to store ephemeral volumes in RBD pool
* Open libvirt ports requred for live migration
* Restrict VNC traffic to management network

Change-Id: I772c6d94de4537ad82d4b62822bdc4f702e8ff56
Implements: blueprint ceph-live-migration
Merge "Make live migrations work for non volume-backed instances with RBD"