Parallel shard load

Loads shards in parallel.

Shards are loaded in parallel both when logplex boots as well as when they are reconfigured in a live system using the `bin/replace_shards`. The system is self-healing now. When a redis shard goes down, logplex will continue to try reconnecting until either the shard comes back or the shard cluster is reconfigured.

The sleep in `logplex_redis_writer` init has been increases slightly to reduce the log spamming during redis downdown.
Because you already reloaded the module, it's possible the `logplex_shard` process has already died. What you're gonna do here if that happened is kill the new one when not needed.

I would possibly recommend trying to do that `whereis(logplex_shard)` before reloading the module, and then adding a blanket `catch` as in `catch exit(whereis(logplex_shard), kill)` right where you are right now to avoid restarting if it's not there.