Adds verfication for Bootable Volume

This submission is to verify the response body of Bootable Volume.
To do so, added required assertions in "test_volumes_get.py"
test script located at ./api/volume and also required modifications
are done in get_volume, list_volumes, list_volumes_with_detail
methods of volumes_client.py(XML)

Implements blueprint: cinder-grizzly1-blueprints-implementation

Change-Id: Id8ac81e268abde1df8d11055079e13e67d4e7ae1
Merge "Adds verfication for Bootable Volume"