ACCUMULO-3242 Add some tests for ZooReaderWriter
ACCUMULO-3242 Rip out the rest of the improper ZK usages in ZooUtil.

The way ZooUtil was written made it really hard to correctly handle
session expirations. Remove ZooKeeper as an argument and use ZooSession
(like ZooReader and ZooReaderWriter) which should correctly account
for a new connection.
ACCUMULO-3242 Add some tests for Retry