Unified network persistence [4.2/4.*] - Upgrade updates running conf

Adds a pre-start task that calls:
vdsm-tool upgrade-to-unified-persistence

The upgrade gathers networking information and updates the running
config of the unified network persistence. Networking persistence
currently uses ifcfg files and after the upgrade will use the
new model. An explanation of how the new persistence model works can
be found at:
http://www.ovirt.org/Feature/NetworkReloaded#Unified_persistence

Change-Id: I051b0f168b6357e60184409845ea410c5891b083
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18425
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>