Set up the event loop for ``actor``.

def setup_event_loop(self, actor):
        '''Set up the event loop for ``actor``.
        '''
        actor.logger = self.cfg.configured_logger('pulsar.%s' % actor.name)
        try:
            loop = asyncio.get_event_loop()
        except RuntimeError:
            if self.cfg and self.cfg.concurrency == 'thread':
                loop = asyncio.new_event_loop()
                asyncio.set_event_loop(loop)
            else:
                raise
        if not hasattr(loop, 'logger'):
            loop.logger = actor.logger
        actor.mailbox = self.create_mailbox(actor, loop)
        return loop