engine: VNIC plug/unplug is incorrectly reported in event log

The terminology should be plug/unplug and not activate/deactivate.

Change-Id: I6f3655a4109712c8368811214d2f5a64e5036810
Bug-Url: https://bugzilla.redhat.com/917522
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>