Auto update nodepool launchers

We previously auto updated nodepool builders but not launchers when new
container images were present. This created confusion over what versions
of nodepool opendev is running. Use the same behavior for both services
now and auto restart them both.

There is a small chance that we can pull in an update that breaks things
so we run serially to avoid the most egregious instances of this
scenario.

Change-Id: Ifc3ca375553527f9a72e4bb1bdb617523a3f269e

playbooks/roles/nodepool-launcher/defaults/main.yaml

@@ -1 +0,0 @@
-nodepool_launcher_start: false

playbooks/roles/nodepool-launcher/tasks/main.yaml

@@ -50,7 +50,6 @@
 
 - name: Start nodepool launcher
   include_tasks: start.yaml
-  when: nodepool_launcher_start | bool
 
 # We can prune here as it should leave the "latest" tagged images
 # as well as the currently running images.

playbooks/service-nodepool.yaml

@@ -10,7 +10,10 @@
 
 - hosts: nodepool-launcher:!disabled
   name: "Configure nodepool launchers"
-  strategy: free
+  # The nodepool-launcher role will restart launchers if new container
+  # images are available. Run serially to ensure we don't kill the entire
+  # cluster if something is terribly wrong.
+  serial: 1
   roles:
     - iptables
     - install-docker

playbooks/zuul/run-base.yaml

@@ -63,7 +63,6 @@
         - group_vars/letsencrypt.yaml
         - group_vars/meetpad.yaml
         - group_vars/jvb.yaml
-        - group_vars/nodepool-launcher.yaml
         - group_vars/refstack.yaml
         - group_vars/registry.yaml
         - group_vars/control-plane-clouds.yaml

playbooks/zuul/templates/group_vars/nodepool-launcher.yaml.j2

@@ -1 +0,0 @@
-nodepool_launcher_start: true