engine: skip CPU checks while updating gluster cluster

While updating a cluster which supports gluster(doesn't support virt),
none of the cpu related checks will be performed.

Change-Id: I7ed98b2cdbcc3006ea42718497051131cbb55711
Bug-Url: https://bugzilla.redhat.com/902882
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>