added support for redis connection pools

[j-castellanos]

To solve this issue #609 in a DRY way I simply wrap all the public methods in the existing redis adapter

[j-castellanos]

@jnunemaker could you rerun the failed test?

[bkeepers]

@j-castellanos Thanks for the PR!

In #826 (review) I offered a couple suggestions of how I think we should approach connection pool support. I don't really love having different adapters Redis depending on if you're using the client directly or a connection pool. I'd rather see Redis and RedisCache updated to work directly with a client or a pool internally, or add a generic ConnectionPool adapter as attempted in #835.

I don't feel strongly between those two approaches, but I would like to make sure we add connection pool support to both Redis and RedisCache at the same time.

Thoughts?

[j-castellanos]

@bkeepers how is this?

[j-castellanos]

Maybe is_a?(ConnectionPool) might be better

[j-castellanos]

@jnunemaker @bkeepers thoughts on this one?

[jnunemaker]

I don't want to add more methods to Flipper::Adapter. I think I'd just make redis and redis cache work with a client or a pool. That seems like easiest way.

def client(&block)
  # if client, then yield that, if connection pool then call with and yield client
end 

# then change all methods that use @client to use client { |c| c.blah... }

We could just abstract a method for getting a client and if adapter was initialized with pool it will use with and a block. If initialize with a client the client would just be used.

I'll make a note to whip something together or anyone else is free to try sooner.