Describe does not consider environment

[timlkelly]

The rake onesie:describe task does not consider the active environment when listing available tasks to run. For instance, if there's a task intended only for production through the allowed_enivornments macro, the DescribeTasks class will still consider it a pending task if you check in development. Which technically it is. However, it will never run in development.

The current design designates the allowed environments in the task class itself and the DescribeTasks uses Manager#pending_tasks to check the available tasks to run, which uses the TaskProxy and so the class itself isn't loaded yet. To solve this, I think we'll need to load the task code to filter the tasks.