NetReload: Moved addNetwork logic to the configurator

This change starts moving the logic of configNetwork API endpoints
towards the configurators.

configureBridge, configureVlan, configureBond and configureNic
after this patch have to take care of the underlying devices
explicitly in the configurator module. However, the underlying
device handling will be abstracted to the network models in a
future patch. Thus, the code of configureBond for IfcfgConfigurator
is gonna be something like:

self.configWriter.addBonding(params)
for slave in bond.slaves:
    slave.configure(params)

Change-Id: I877eddc07a17f0bdd376df7bab8b19ffe52f72ba
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>