engine: Clarifying CDA message of adding vnic profile

The patch clarifies the can-do-action of adding a vnic profile
to a non-vm network.

Change-Id: I4e829ffb118ce066a266196286b9b7ea8e578ecc
Bug-Url: https://bugzilla.redhat.com/1012009
Signed-off-by: Moti Asayag <masayag@redhat.com>