def resolve_retry_delay(delay)
      if delay.respond_to?(:queue_retry_delay)
        resolve_retry_delay(delay.queue_retry_delay)
      elsif delay.is_a?(Integer) # numerical
        delay
      else # default
        Backburner.configuration.retry_delay
      end
    end
Resolves retry delay based on the value given. Can be integer, a class or nothing

@example
resolve_retry_delay(5) => 5
resolve_retry_delay(FooBar) => <queue retry_delay>
resolve_retry_delay(nil) => <default retry_delay>