Renew slots when MOVED occured during request to Cluster

* It's suggested by http://redis.io/topics/cluster-spec
** antirez/redis-rb-cluster implementation does it, too
* Since Redis 3.0-beta 7 introduces CLUSTER SLOTS, it becomes easier
* FIXME: It's fully synchronized, so it hurts performance (somewhat poor implementation)
** We can try Reader / Writer strategy to make lock waiting make shorter
Replace synchronized keyword lock to ReaderWriterLock
Re-format source to respect Jedis convention