Improve connection handling when bootstrap list is invalid (#1507)
Improve connection handling when bootstrap list is invalid (#1507)

* only perform single dns lookup for connect_blocking()
* fix blocking timeout in check_version()
ohmu/kafka-python,DataDog/kafka-python,wikimedia/operations-debs-python-kafka,ohmu/kafka-python,Aloomaio/kafka-python,scrapinghub/kafka-python,dpkp/kafka-python,wikimedia/operations-debs-python-kafka,mumrah/kafka-python,Aloomaio/kafka-python,scrapinghub/kafka-python,Yelp/kafka-python,mumrah/kafka-python,dpkp/kafka-python,Yelp/kafka-python