ZooKeeper reconfig API backward compatibility fix

ZOOKEEPER-2014 moved the reconfig() methods into a new class, ZooKeeperAdmin. It appears this was done to document that these are methods have access restrictions. However, this change breaks Apache Curator (and possibly other clients). Curator APIs will have to be changed and/or special methods need to be added. A breaking change of this kind should only be done when the benefit is overwhelming. In this case, the same information can be conveyed with documentation and possibly a deprecation notice.

Revert the creation of the ZooKeeperAdmin class and move the reconfig() methods back to the ZooKeeper class with additional documentation.