Zookeeper, etcd support multiple ips but datastore.newClient only takes one.

This can cause inability to restart docker if the Zookeeper or etcd peer specified in kvstore argument goes down -- even if the other n-1 are up.

Further it appears that this list is the complete list of alternate backends that go-zookeeper/etcd client libraries will try in the event of a failure, meaning that if only one is specified it constitutes a single point of failure.