Enable the server personality feature

http://docs.openstack.org/api/openstack-compute/2/content/Server_Personality-d1e2543.html
-Use different approaches for different OS:
 CentOS - use libguestfs
 Ubuntu - use NBD due to the problems with libguestfs

Change-Id: Id2139b415af3f8835a6d4e9ee90e81121caf7c95
Closes-bug: #1335697
Merge "Enable the server personality feature" into stable/5.1