Unified network persistence [4.1/4.*] - Upgrade mechanism

Unified network persistence feature:
http://www.ovirt.org/Feature/NetworkReloaded#Unified_persistence

This patch is the first of two patches that implement an upgrade
that is run the first time VDSM that uses unified network
persistence is started. The goal is to look at the current
host networking configuration and populate the running
and persistent configurations.

Change-Id: Iba3c9c34f03134c192db1c2add31084824e195d9
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17726
Reviewed-by: Dan Kenigsberg <danken@redhat.com>