AbstractAdapter fixes for Rails 5

[calh]

Starting in rails 5.0, the initializer for AbstractAdapter changed

rails/rails@8c53b20

This makes the ibm_db gem compatible with the latest octopus sharding gem version. The line:

super(@connection, logger, config)

fixes the rails 5 AbstractAdapter change, and the line

@config = config

backpatches the issue for rails 3 and 4, so that the octopus gem and ibm_db will still work with older versions of rails.

[akhilravuri1]

Thanks for raising the pull request. In the latest release we have added support for the rails 6 version also.