Allow the server administrator to enforce a particular root on specific authenticated users.
ZOOKEEPER-237 implements the client side of this - the client can set a chroot, however this doesn't allow
someone like an administrator to enforce the root.
We should add the ability to the server to verify that all accesses are to a particular root.
We currently have ACLs which provide essentially this, however there are a few small issues where root enforcement
would be useful from server operator perspective.