Since f21 the kernel modules are split to multiple packages
and by default just the core modules gets installed.

nova requires iscsi_tcp module for attaching a volume
from any iscsi source (default cinder lvm setup).

On el7 it is not required.

Change-Id: I31705720ade5defd1b6d4b95bc51c2a11a5f0364
Related-Bug: #1429504