Add tests for writing messages
Smarter Message.toString()

The current one will blow up Splitlog Logback logs when the Message has
a stack trace.
Prevent tests from interfering with each other
Always run tests in alphabetical order
More logging in Tailer
Fix test post toString() refactor.
Enable test that was disabled for no reason.
testWriteMessages() no longer relies on predefined file
Flush written messages immediately
Async logging in the tests