RedisLock.obtainLock() doesn't provide desired distributed lock guarantee

Looks like WATCH doesn't provide good isolation when the call is performed concurrently at the same time from different Threads.
Or we don't use it correctly...

I can simply reproduce it with the @Repeat(10) for the failed test AggregatorWithRedisLocksTests.testDistributedAggregator().

Reconsider locking algorithm as it is recommended by Redis SET command: http://redis.io/commands/set