[rackspace|compute] Fix typo in attachments model.
[rackspace|compute] Handle malformed API responses.

When deleting a Cloud Network, the API returns a plain text
response even when the Content-Type is set to
application/json. In the event of a JSON parsing error, this
change sets the request body to an empty hash.
[rackspace|networks] Add Cloud Networks requests.
[rackspace|networks] Add networks model and collection.
[rackspace|compute] Update server to use default networks.

Rackspace Cloud Networks uses hard-coded UUIDs for
identifying public net and service net. This defaults the
network array for new servers to use public net and service
net.
[rackspace|compute] Allow custom network on server.

When creating a new server, you can now pass an array of
network IDs to which that server has access. If no networks
are specified, it default to public net and service net.
[rackspace|networks] Add mock responses.
Merge pull request #1541 from bradgignac/rackspace-cloud-networks

[rackspace|networks] Rackspace Cloud Networks