Add support for Resque Pool when started via Rake task

When [Resque Pool is started through a rake task](https://github.com/nevans/resque-pool#other-features), NewRelic's RPM local environment inspection is [failing to configure the `:resque` detector](https://github.com/newrelic/rpm/blob/master/lib/new_relic/local_environment.rb#L154-L156).

Here's an attempt of making best effort a little bit better ;)