move make_key function to BaseCache and remove namespacing logic from Clients

[2ykwang]

django-redis the make_key implementation across individual clients (such as ShardClient),

leading to the following problems:

• make_key should be defined in RedisCache (which inherits from BaseCache) and used consistently for all cache operations.
• Client classes should not handle key namespacing logic.

How about handling make key name in RedisCache class