[Redis] RedisClientFactory needs some rework

[Arsnael]

After checking the code around, couple of things are wrong with RedisClientFactory.

Redis cluster:

• no ssl is setup with client if specified in redis conf

Redis master/replica:

• readFrom, ioThreads and workerThreads not used in redis client setup

Redis sentinel:

• readFrom, ioThreads and workerThreads not used in redis client setup

Redis sentinel and master/replica have the exact same client setup (copy/paste)...

Regarding healthcheck timeouts, some seem setup with the client (standalone, cluster), some seem setup from the healthcheck (sentinel, master/replica)

Might be other things... Have a complete look other the configuration and factory of all redis topologies again and try to give it sense, with proper tests.

And try to see if proper redis client setup would help in the end solve this issue => linagora/tmail-backend#1585

[Arsnael]

WIP Redis backend tests refactoring: apache#2668

[Arsnael]

SSL for redis cluster: apache#2669

[Arsnael]

Except for SSL I think, not a priority for the rest. Putting back to the todo