Some fixes to connection pooling
Some fixes to connection pooling

Pick up some fixes from Consul:

* If a stream returns an EOF error, clear session from cache/pool and start a
new one.
* Close the codec when closing StreamClient

dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,dvusboy/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad