this approach totally removes the process of reading and writing stdout
files on the local file system at settings.JOBOUTPUT_ROOT when jobs are
run; now stdout content is only written on-demand as it's fetched for
the deprecated `stdout` endpoint
see: https://github.com/ansible/awx/issues/200
* introduces three new models: `ProjectUpdateEvent`,
`InventoryUpdateEvent`, and `SystemJobEvent`
* simplifies the stdout callback management in `tasks.py` - now _all_
job run types capture and emit events to the callback receiver
* supports stdout reconstruction from events for stdout downloads for
_all_ job types
* configures `ProjectUpdate` runs to configure the awx display callback
(so we can capture real playbook events for `project_update.yml`)
* ProjectUpdate, InventoryUpdate, and SystemJob runs no longer write
text blobs to the deprecated `main_unifiedjob.result_stdout_text` column
see: https://github.com/ansible/awx/issues/200
Christian Adams
Jim Ladd
Ryan Petrello
Jake McDermott
AlanCoding