Add *_network params and logic.

The purpose of this is to allow a user to specify what they know, which
sometimes is not the nic (which may not be known to them at setup time until
after the machine is provisioned).  They should be able to provide the network
they know a nic should be in though, and we can use this to figure out which nic
got attached to that network.
Merge pull request #179 from jguiditta/infer_nic

Add *_network params and logic.