Add one more slave to the ceph test

To get possible instance creation in verification
add 1 slave to the ceph tests

Also change update disk value
to avaid unallocated space, because by default we
have 50 Gb on each slave

Change-Id: Ibd7ad3b38ce1e8bad3cd928047f04d4c8cc8d47e
Closes-Bug: bug #1260677
Merge "Add one more slave to the ceph test"