[TORQUE-986] description option not allowed in job section of DSL config

This fixes the issue. Added a unit test and modified one integration test to check this.

Additionally made sure the description is set by running this app:

torquebox.rb:
```ruby
TorqueBox.configure do
  job Dummy do
    cron '*/10 * * * * ?'
    name 'dummy'
    description 'A description for a job'
  end
end
````

dummy.rb:
```ruby
class Dummy
  def run
    job = TorqueBox::ScheduledJob.lookup('dummy')
    puts job.name
    puts job.description
    puts "Dummy job executed"
  end
end
````