This updates the ZooKeeper class to inherit from ZooKeeperBase
and utilize its connection methods.
It also moves the connection loss detection used by the builder
to be more localized and removes unused methods.
We have made many improvements to connection handling in Zuul.
Bring those back to Nodepool by copying over the zuul/zk directory
which has our base ZK connection classes.
This will enable us to bring other Zuul classes over, such as the
The existing connection-related code is removed and the remaining
model-style code is moved to nodepool.zk.zookeeper. Almost every
file imported the model as nodepool.zk, so import adjustments are
made to compensate while keeping the code more or less as-is.