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

awx/playbooks/clean_isolated.yml

@@ -10,7 +10,7 @@
   tasks:
 
     - name: cancel the job
-      command: "systemctl stop playbook@{{job_id}}.service"
+      command: "tower-expect stop {{job_id}}"
       ignore_errors: yes
 
     - name: remove build artifacts