* set a more reasonable default `AWX_ISOLATED_CHECK_INTERVAL`
* make manual cancellation work for high values of
`AWX_ISOLATED_CHECK_INTERVAL`
* remove the `/tmp/ansible_tower/jobs/` symlink directory
see: #6616
instead of launching isolated tasks via `systemctl`, treat
`awx.main.isolated.run` as an executable that knows how to daemonize
additionally, add `setup.py isolated_build` for isolated Tower source
distribution