Improve use of structured logging in webapi tests.

Avoid using a mix of stdlib logging and structured logging.

Disconnect the websockets handler when stopping the server.

Only send relevant messages over the websocket.
Remove failures from omni-analyzer
fixup! Improve use of structured logging in webapi tests.
Merge pull request #154 from mozilla-b2g/jgraham/webapi_structured_improvements

Improve use of structured logging in webapi tests.
Merge pull request #155 from dminor/bug-1041502-fix

Remove failures from omni-analyzer