cbauth-external should allow requests during reconnection

The current implementation of external authentication inside of cbauth follows the 'global' paradigm of the typical cbauth implementation. This leads to the behaviour where attempting to connect cbauth to a new node requires that the existing instance be disconnected before the new connections can be established. Due to the neccessity of having the user of cbauth-external (in this case, CNG) track the topology of the cluster and reconnect to a new node whenever the existing node is being rebalanced out it leads to a period of time where CNG is unable to execute any requests since it does not have an established connection to any node.