def _run_grid_multiprocess(self, func, iterables):
multiprocessing.freeze_support()<EOL>pool = multiprocessing.Pool()        <EOL>pool_tracers = pool.map(func, iterables)<EOL>pool.close()<EOL>pool.join()<EOL>self.tracers = dict(zip(self._default_devices, pool_tracers))<EOL>
running case with mutil process to support selenium grid-mode(multiple web) and appium grid-mode(multiple devices). 
        @param func:  function object
        @param iterables:  iterable objects