Add facility to wait for a certain number of messages to DeviceTestServer
WIP for an ioloop manager that can be shared between client and server implementations
Create a new future in handle_message.

Need to create a new future before returning it to KATCPserver, or it will also
get the exceptions handled by send_reply()
multi-stopping fixup
Reduce logging noise by having mass_send_messages skip closed connections
Improve test reliability by increasing silly short timeout
Merge pull request #26 from ska-sa/factor-ioloop-manager

Factor ioloop manager
Beginning of tornado client WIP
Client refactor WIP
WIP for an ioloop manager that can be shared between client and server implementations
Tornado based katcp client WIP