Message field doesn't expand "%s" style format strings

[johnedo1234]

We're seeing log messages coming from JBoss with unexpanded "%s" format strings. Since those messages aren't coming from our code, we can't change them to use the format strings expected by the logstash-util-formatter.

[johnedo1234]

Think the formatter should also support "%s"-style format strings and expand them properly.

[johnedo1234]

Fixed and submitted pull request: #12

If regular formatting produces no change to the message and there are actually parameters, falls back to String.format(). If that fails, just returns the original message.