DATAREDIS-261 - Upgrade to commons-pool2.

`JRedisPool` and `DefaultLettucePool` have been migrated to `commons-pool2`.

`PoolConfig` has been deprecated, and will be removed in `1.4`, as all required operations are available via `GenericObjectPoolConfig`.

Along the way a minor bug within `LettuceConnection` has been resolved, which prevented `RedisAsyncConnections` from being properly closed/returned to pool.