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/run_isolated.yml

@@ -36,7 +36,7 @@
       command: "mkfifo /tmp/ansible_tower/jobs/{{job_id}}/env"
 
     - name: spawn the playbook
-      command: "systemctl start playbook@{{job_id}}.service"
+      command: "tower-expect start {{job_id}}"
 
     - name: write the secret environment data
       mkfifo: