Support for PSYNC about redis-py-cluster

[Grokzen]

@NirmalP29 The simplest answer is that you don't do it through this class as the more management style of commands is absolute best suited to be done via the normal Redis class instance directly towards the node you want to interact with.

But you can manually dig up the Redis object instance for the master node if you try to look for it manually in the connection pool object ClusterConnectionPool and the internal object nodes and you should be able to find the Redis instance for your master node that you want to send this to.

I highly recommend that you migrate over to a later version of redis-py that now supports clustering based on the work from this repo and attempt to solve it through what new code they have written to support node targeting solutions.