refactor: storage-broker should be given a client, also no circular ref

[meejah]

See create_no_network_client in test/no_network.py -- it has to create a storage-broker to give to the client, but then also has to give/change a "client" ref to the storage-broker

This is bad for two reasons:

• there's a circular reference
• a _NoNetworkClient isn't "really" set up until someone fixes this ref from outside..