feat: add logging to proxy

Adds reasonable logging to the proxy, especially at the transport
layer and for cache debugging.

Mostly imitates the logging style used by the queues server.

Partially-Implements blueprint placement-service
Change-Id: If5490a3b18bf660e9c7a57f47959eedacc936b48
Closes-Bug: 1230379

Change-Id: I9113f4b4e4b02de62b7470d3dca4d08fdd0769cc