engine: Enable detaching network from host when a VM has an unplugged
VNIC profile of that network

Enable detaching network from host when a VM has an unplugged VNIC
profile of that network.

Change-Id: I10db794df55b25925423166d33549b92856e9dd0
Bug-Url: https://bugzilla.redhat.com/1115101
Signed-off-by: Yevgeny Zaspitsky <yzaspits@redhat.com>