VMWare driver to use current nova.network.model

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

Fixes: bug 1112655
Change-Id: I7f4b39cd5add7d3cf7dcf485eb9855d0354f332c