engine_page: use vdsm to detect mgmt interface

Replace the method to detect the mgmt interface by VDSM.

Change-Id: I9e1b69c0f465f1e38779e451777cae67bd4cde40
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1058257
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>