Add volume backup description parameter
Add volume backup description parameter

Update "test_volume_backup_create_get_detailed_list_restore_delete"
testcase to verifiy volume backup description parameter.

Change-Id: Ib8de9029d61cbce8519eafa38d98428fa7155ea6

vedujoshi/tempest,masayukig/tempest,masayukig/tempest,openstack/tempest,vedujoshi/tempest,cisco-openstack/tempest,Juniper/tempest,Juniper/tempest,openstack/tempest,cisco-openstack/tempest