Support Distributed locks with Redis

[pendula95]

Add support to:

https://redis.io/topics/distlock

[pendula95]

I have misinterpreted the usage of Lock for Redis. As this feature is purely business logic related and just uses Redis as implementation for the lock this request can be discarded as vertx-redis client currently aims to cover only Redis protocol and not potentials usecases behind. Your call @pmlopes

[pmlopes]

I think we could implement this purely as a helper class as it could open the door to other things, for example, a redis backed cluster manager, as it would provide the basic foundation blocks needed for such implementation.