issue91: do not accept resume/suspend when a task is ongoing.

That's what we plan to do eventually, but it's not needed in your case

You can use multiple values in a when, and your method would be

```ruby
b.use Call, ReadState do |env, b2|
  case env[:machine_state_id] 
  when :not_created
    b2.use Message, I18n.t('vagrant_openstack.not_created')
  when :suspended
    b2.use Message, I18n.t('vagrant_openstack.already_suspended')
  when :active || :resumed
    b2.use Suspend
  else
    b2.use Message, I18n.t('vagrant_openstack.ongoing_task_or_not_resumed')
  end
end
```
which looks more readable to me

or put you condition in the else, even if that's not the way I would prefer