Raise log levels for locator errors.

Squelch `io.EOF` errors for closed sockets.
`UpdateHandler`: Avoid hangs for bad primary keys.
Worker: Clean up message parsing.

* Simplify `isPingBody`. Use `json.Compact` instead of tokenizing the
  byte slice.
* Fix an issue that treated arbitrary one-byte slices as pings.
Merge pull request #130 from mozilla-services/feature/level-up-logging

Raise log levels for locator errors
Add tests for malformed endpoint keys.
Merge pull request #131 from mozilla-services/feature/parse-cleanup

Clean up message parsing
Add logging.name setting.