Adding network and virtual_interface commands to the cloud module

If you use things like rackspace, the extensions will need to be specified in
in the extensions.

```
my-nova: 
  minion:
    mine_functions:
      network.ip_addrs: []
    startup_states: sls
    sls_list:
      - cloud.novaclient
  identity_url: 'https://identity.api.rackspacecloud.com/v2.0/'
  extensions:
    networks: os_networksv2_python_novaclient_ext
    virtual_interfaces: os_virtual_interfacesv2_python_novaclient_ext
  protocol: ipv4
  compute_region: DFW
  user: USER
  tenant: TENANT
  provider: nova
  api_key: APIKEY
  os_auth_plugin: rackspace
  wait_for_ip_timeout: 6000
```