Pass extra named args from RedisCache.__init__ to the Redis.__init__

The Redis can be accessed not only via TCP socket but also by UNIX socket: [`unix_socket_path`](https://github.com/andymccurdy/redis-py#connections) parameter allows this.
But it is impossible now to pass such argument to `Redis` class through `RedisCache` class.

This change allows to feed `Redis` with any extra argument like `connection_pool` or `decode_responses`.