engine: Fail import vm if mac addresses are missing

When a vm is imported as new entity, there is a
mac allocation for any imported vnic. If the mac
addresses pool has insufficient addresses, the
action fails during the execution. The patch fails
the operation on can-do-action with a proper message
to the user for the failure reason.

Change-Id: I86680baa28c22def751c9c092f4cfde26ab1c45c
Bug-Url: https://bugzilla.redhat.com/1008168
Signed-off-by: Moti Asayag <masayag@redhat.com>