Use computes + control for NUM_OS_SYSTEM

This is not going to work when we want to make our HA
CSIT work, since I think Apex will be having 3
openstack control nodes, and our CSIT won't know what
to do with '5' (3 control + 2 compute) openstack
nodes. But, we can cross that bridge when we get
there.

Change-Id: I9c74b2ec73e5af0039d93f9ed812fc3c100a3e4a
Signed-off-by: Jamo Luhrsen <jluhrsen@redhat.com>