ZooKeeperClient: Add chroot support

From #52.

Adds two constructors that take an extra `String chroot` argument, which must be non-null, and defaults to `""`. `chroot` is then appended on to the end of `this.zooKeeperServers`.

Apologies: I wasn't able to compile or run this. I fought with manually injecting some dependencies into ivy (javax.jms, com.sun.jdmk, and com.sun.jmx), but then I gave up after it failed to find thrift (`Do not have thrift binary for os: Mac OS X 10.8 x86_64`). But it's a pretty simple change.