[system-tests]Add test for cinder+rbd cow regression

[Dmitry Borodaenko]

Bug #1373096 was a regression of copy-on-write behaviour when creating a Cinder volume from a Glance image, with both using Ceph RBD backend.

We need to add a check to our ceph system test to confirm that the RBD object created for a new volume based on a RAW Glance image has a parent (can be verified using "rbd ls -l volumes/<volume-id>" command).

[Dmitry Borodaenko (angdraug)]

Bug description updated to highlight that you should be creating a Cinder volume from a RAW Glance image. If image in Glance is QCOW2 (which is the format Fuel uses for its CirrOS image), copy-on-write will still not happen.

[Dmitry Borodaenko (angdraug)]

Here's an example of rbd output for a cloned image with a parent:

 [root@node-10 ~]# rbd info volumes/volume-1981a808-fc21-4a2d-aaf1-7052a4bbb0ee
rbd image 'volume-1981a808-fc21-4a2d-aaf1-7052a4bbb0ee':
       size 1024 MB in 128 objects
       order 23 (8192 kB objects)
       block_name_prefix: rbd_data.163e17d07053
       format: 2
       features: layering
       parent: images/d6860d44-0dfd-48a2-bb28-a44c24f23ba5@snap
       overlap: 40162 kB

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/184908