Test `GET /connection` more

[sajith]

The handler and the test are pretty skeletal at present. We need to make sure things work as expected under a variety of scenarios:

• Do GET /connection when nothing has been set up.
• Do GET /connection after a connection has been requested, when all expected topologies are present.
• We can find actual status of connection requests (failures, successes, progress).
• Refine the responses as necessary (with JSON payload, when required).