Start monitoring for hanging threads.

    seconds_frozen - How much time should thread hang to activate
    printing stack trace - default(10)

    tests_interval - Sleep time of monitoring thread (in milliseconds) 
    - default(100)

def start_monitoring(seconds_frozen=SECONDS_FROZEN,
                     test_interval=TEST_INTERVAL):
    """Start monitoring for hanging threads.

    seconds_frozen - How much time should thread hang to activate
    printing stack trace - default(10)

    tests_interval - Sleep time of monitoring thread (in milliseconds) 
    - default(100)
    """
    
    thread = StoppableThread(target=monitor, args=(seconds_frozen,
                                                   test_interval))
    thread.daemon = True
    thread.start()
    return thread