process_all_frames() now catches up with the live stream afters lowing
down to process all the frames.

However, there should be a way to do the same thing by substituting the
next line for something more efficient:
      self.restart_source_bin()
catch_up_live_stream() now has the code from restart_ource_bin() without
the underrun handler. This fixes the constant underruns and hanging that
it was causing between the first step and the second of the test.