JedisSentinelPool now takes care of multi failover

* Now Pool.initPool() call closeInternalPool(), instead of destroy()
** calling destroy() in Pool.initPool() may have side effect, and JedisSentinelPool did
* modify unit test to test failover twice (needs +1 slave)
** modify configurations for additional slave
Merge branch 'master' of https://github.com/xetorthio/jedis
Added test from pull request #429.