Fix abstract class descendants not inheriting custom connection

[codygustafson]

Fix thiagopradi#219

I'm adding this in to our REPO to fix what was laid out in the original branch.

[joshcom]

Boy, we are far behind! Makes sense though, great find.

[codygustafson]

Yeah, I'm looking into what would prevent us from upgrading our version here. As far as I can tell a lot of our fixes have been implemented in different ways in the official gem.

[calh]

(I'm working with Cody right now on trying out my master branch of Octopus with all of my fun fixes)

[wlmcewen]

I believe @calh has actually been using the official gem and reporting issues he's encountered with DB2 specifically.

thiagopradi#531
thiagopradi#538
thiagopradi#526

[calh]

Teaser: you can add custom load balancers for slave groups:
calh@58df2cb
https://github.com/calh/octopus/blob/master/lib/octopus/slave_group.rb
https://github.com/calh/octopus/blob/master/lib/octopus/load_balancing/round_robin.rb

https://github.com/calh/octopus/blob/master/spec/octopus/db2_spec.rb#L16
https://github.com/calh/octopus/blob/master/spec/config/shards.yml#L259

[wlmcewen]

LGTM. To be clear, I have no opposition to moving to the latest version, especially with the tons of work Cal has put in working with this gem there.