BareMetal driver to use current nova.network.model

* Updated tests to use classes from nova.network.model instead of legacy
  "network,mapping" tuple.
* Modified baremetal/{driver,pxe,vif_driver}.py to use classes from
  nova.network.model instead of legacy "network,mapping" tuple.

Change-Id: I8b4efa4bfb804c658b29d80373d9d0e4572b8e20
Fixes: bug 1112642