isolated ramparts: replace systemd unit with a tower-expect binary

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

tools/docker-isolated/README.md

@@ -66,6 +66,6 @@ This should give a shell to the `tools_isolated_1` container, as the
 The following command would run the playbook for job 57.
 
 ```bash
-systemctl start playbook@57.service
+tower-expect start 57
 ```