Migration plan:
* add zk* to emergency
* copy data files on each node to a safe place for DR backup
* make a json data backup: zk-shell localhost:2181 --run-once 'mirror / json://!tmp!zookeeper-backup.json/'
* manually run a modified playbook to set up the docker infra without starting containers
* rolling restart; for each node:
* stop zk
* split data and log files and move them to new locations
* remove zk packages
* start zk containers
* remove from emergency; land this change.
Change-Id: Ic06c9cf9604402aa8eb4bb79238021c14c5d9563
42574b2b37