fix(core): when connection fails, close the ConnectionHandler (#577) (#579)
fix(core): when connection fails, close the ConnectionHandler (#577) (#579)

When connection attempts fail repeatedly (e.g. all ZK servers are
unavailable), eventually the socketpair in the ConnectionHandler fills
up, and the Client gets stuck trying to write a single byte to the
socketpair.

Avoid this by ensuring we close the socketpair on a failed connection
attempt.
python-zk/kazoo,python-zk/kazoo