engine: Bind port to agent when port is being activated

When using the ml2 core plugin, the activated port should
be associated with the host on which it has been scheduled.

Bug-Url: http://bugzilla.redhat.com/1078862
Change-Id: I0cb5bf95054b6d2711f88a09d374a74f156a4055
Signed-off-by: Moti Asayag <masayag@redhat.com>