engine: Collect stats before activating host

When the host moves to non operational due to a
required interface in down state, the host statistics
should be collected and examined before attempting
to activate the host.

Change-Id: Id3de8a3ccb1084f8be8f9c3213f797146f8f0b36
Bug-Url: https://bugzilla.redhat.com/1070260
Signed-off-by: Moti Asayag <masayag@redhat.com>