Add a Redis worker

Gathers information about Redis (version, memory, OS, replication,
sample keys) and adds it to the extra data. Not hooked in to any UI
triggers yet, though. Run it like so:

Port.where(product: 'Redis key-value store').each {|p|
Sidekiq::Client.enqueue(RedisWorker, p.id, p.ip_address.to_s, p.number)
}

Note that running it multiple times will end up with multiple copies of
the results. This should probably be fixed at some point.
Display newlines in the extra info correctly.