[Async] Support for transactions in async RedisCluster client (redis#3649)

* Refactored ClusterPipeline

* Added some basic test coverage

* [Async] Multi Exec on cluster

* Codestyle fix

* Fixed variables access

* Fixed another variable access

* Fixes according to comments

* Changed usage of protected properties

* Revert port changes

* Remove duplicated code, added TODO's

Author: vladvildanov