Server create will only process "networks" if os-networks is loaded.

When working with a quantum configuration and multiple networks you
have to be able to pass in the requested network to avoid instances
being attached to all networks, so this part of the request isn't
really optional in practice

However the os-network extension is not fully compatible with
quantum, and the operations do map very well. For example:

- Network creation has a set of options that are pretty nova-nets
  centric (such as VLAN)

- Network creation is limited to admins

- Network association and dis-association from projects is not
  the quantum model

- cidr from quantum is not shown correctly in the output of nova
  network-list and network-show

Rather than needing the os-networks extension to loaded and
thereby exposing a bunch of calls that don't really map to
quantum, it would be better to also allow processing of "networks"
when the network api is configured to be quantum

Fixes bug #1150250

Change-Id: I0cc1faf6417d7a004dd9f0ff772860237fc94c57
Merge "Server create will only process "networks" if os-networks is loaded."