Fixed: When saving properties in ZooKeeper nodes, empty properties
       were encoded as empty strings.  When Kazoo saves empty strings,
       it does so in a way that causes the ZooKeeper C client (or at
       least the Python C binding) to see semi-random data, sometimes
       including data written previously to other nodes.  This can
       cause havoc when data for one node leaks into another.

       Now, we save enpty propeties as '{}'.