Optionally exclude queues by worker

[adamonduty]

This is an another attempt at pull #28 with tests (credit to @arjes for tracking down the code change). It also should be compatible with current/previous versions of DJ by using respond_to?. Assuming this pull is acceptable, I'll submit another to DJ proper to add the cli options.

[coveralls]

Changes Unknown when pulling 1289acd on adamonduty:exclude_queues into * on collectiveidea:master*.

[derekrockwell]

👍

[derekrockwell]

I've created a fork for a purpose similar to this with the notable difference that the query is

ready_scope = ready_scope.where('queue NOT IN (?) OR queue IS NULL', Worker.except_queues)

In order to pick up nameless queue jobs which would be restricted from the not in query comparing to nil, but would still make sense in an 'except queue' workflow imo.

[adamonduty]

@derekrockwell Looks good to me! I did the same and pushed the branch.