Cannot get Cloud Networks client using a context

[rs-randallburt]

When using contexts:

ctx = pyrax.create_context('rackspace')
ctx.auth_with_token(...)

The following call fails because there isn't a "networks" entry in the service catalog:

ctx.get_client("networks", "IAD")

The non-contextual pyrax has special handling of the "compute:network" type that uses the compute endpoint to get a networks client. It would be helpful if this were the case with contexts as well.

[EdLeafe]

Good catch. I'll have to add some special-case code to handle this.