NetReload: netmodels for addNetwork

This patch defines the netwok entities that we use in oVirt:

- NetDevice,
- Bridge,
- Vlan,
- Bond,
- Nic

These entities are now responsible for their underlying devices for
the addNetwork step.

The interaction is as follows:

1. addNetwork -(generates netmodels via)-> objectivizeNetwork
2. "configure(logical_net)" is called on the top network device,
3. The top network device calls configure for its device type on the
   configurator, that in turn calls configure in any underlying device.

In a following patch, they shall take
responsibility as well for network deleting.

Change-Id: Iba5c5b84760e27245cbe34c3b290c54e51278e72
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/14303
Reviewed-by: Dan Kenigsberg <danken@redhat.com>