engine: Prevent implicit usage of port mirroring

The patch denies attempt of an imported vm to use
a vnic profile by the imported vnic if the vm or
template haven't explicitly stated that the exact
vnic profile to be used.

Change-Id: I4f47627642d38fd537dbeed8f1b41a0849566063
Bug-Url: https://bugzilla.redhat.com/1001068
Signed-off-by: Moti Asayag <masayag@redhat.com>