Switch to a logger rather than straight console output.

We're still outputing to the console (and letting supervisor log to
files for us), but this adds useful timestamps and error log levels to
the output.
Improve mongo logging, so we only log unexpected disconnects.

This cleans things up a bit so normal shutdown doesn't spew mongo
disconnect errors.
Improve logging during tests, so debug logs can be output to a file.

This is preferable for tests, so we don't have to always worry about
having quiet output and can better debug things during testing.
Bump api-umbrella-gatekeeper to v0.2.2.