Improve JRuby Support

Recent gem releases have introduced a few incompatibilities with JRuby that should be resolved:

- [x] the UDPReporter is broken
- [x] Don't bundle the c-extension for JRuby
- [x] Support X-TV-Meta header
- [x] Use the new Joboe ReporterFactory instead of direct invocation of UDPReporter
- [x] Agent initialization fails when bundler is on the command line
- [x] Add JRuby test suite support
- [x] Add JRuby to list of Travis tested Ruby versions