Unified persistence [3/4] - Restore network config

Add vdsm-restore-net-config support for unified persistence.
It relies on flushing of configurator-specific persistence, i.e.,
each configurator should remove its persisted conf, leaving
only unified persistence as source of persistence.

After the configurator persistence is flushed, the unified
persisted nets and bonds are passed to a setupNetworks call.

Since we want vdsm-restore-net-config to be run at boot after
libvirtd but before vdsmd listens, the service was removed
and it was integrated as one of the start tasks. However, we
must run vdsm-restore-net-config only during boot time, and
not on every vdsmd restart.

If the restoration is run via vdsmd_init_common.sh we touch
/var/run/vdsm/nets_restored that, if present, marks to future
vdsmd restarts that service boot-time network restoration is
no longer expected nor in order.

The user can explicitly restore the nets by calling
/usr/share/vdsm/vdsm-restore-net-config or via vdsm-tool:
vdsm-tool restore-nets

Change-Id: I73462b160ecfbaa7efe71eed905a3bbd69ee6c23
Signed-off-by: Assaf Muller <amuller@redhat.com>
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17010
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>