engine: Do not access storage domain for gluster only hosts

Gluster hosts are moved to non-operation as they cannot
access the storage domain. This check is not necessary
for gluster hosts

Change-Id: Ic6e9c02bf68146975987c6cb48cccf5c198a2e5b
Bug-Url: https://bugzilla.redhat.com/1105513
Signed-off-by: Sahina Bose <sabose@redhat.com>