Added a method to run the js tests external process in a timeout-monitored way,
so if the java process running the tests takes longer than expected, it gets
killed.
Removed the capture_output option when running the runner. Runner.run() now
returns success (True/False) depending on the tests run status:
- False if the process running the tests timed out
- False if the process did not time out but any js tests failed
- True if the process did not time out and no js tests failed