Add a function to return the class name of the selected poller in the IOLoop and fix the KQueue poller.
Add a function to return the class name of the selected poller in the IOLoop and fix the KQueue poller.

fkarb/pika-python3,Zephor5/pika,knowsis/pika,benjamin9999/pika,vrtsystems/pika,vitaly-krugl/pika,skftn/pika,Tarsbot/pika,renshawbay/pika-python3,shinji-s/pika,zixiliuyue/pika,reddec/pika,jstnlef/pika,pika/pika,hugoxia/pika