pass network iface request through from app layer to `zmq_bind`

[andre-merzky]

See #444 - we have contradictory requirement for Anvil and Amarel, and the default iface list will, depending on the order, only work on one of them. The get_hostip() call can overwrite that list with the req parameter all right - but we don't pass that parameter through the ZMQ layer just yet, so RP cannot specify the preferred interface. This needs to be exposed, preferably by changing ru.config.default settings.

[andre-merzky]

@AymenFJA , @mtitov : I hope you don't mind, I pushed the config changes right on top of Aymen's PR. The following code in RP should now set the default interface for ZMQ:

dc = ru.config.DefaultConfig()
dc['iface'] = 'ib0'

so we can no expose that as a resource config option.