ZK client times out against zk 3.3 and 3.4

[spacejam]

My friend @dallasmarlow told me that he has been seeing client timeouts against zk 3.3 and 3.4 using this zk client, as the session timeout is not being properly respected. This is causing his ephemeral znodes to constantly be invalidated. We need to:

1. reproduce the timeouts
2. fix the zk dep or set up a background pinger that does something simple like perform a get on the root znode every few seconds (maybe every 10s with a small amount of splaying) to prevent the session from timing out due to failing to respect the heartbeat interval.

[dallasmarlow]

@spacejam https://github.com/samuel/go-zookeeper/issues/82

it looks like this doesn't cause an issue for the mesos-go client in most cases due to it's rewatch interval being so low (statically configured to 200ms), which in turn is acting like a heartbeat and keeping the session alive.

[tsenart]

@spacejam: Ping.