Run zuul cluster reboots and updates automatically

This adds a weekly cronjob that will reboot and update our entire zuul
cluster gracefully. The time frame chosen for this should be after North
America begins its weekend and before Europe starts their week. The idea
is that we're doing this during the quiet time of our week.

Change-Id: Ib9a54f273e11744fa1ddbf367c291289f86bddb7

playbooks/service-bridge.yaml

@@ -39,3 +39,23 @@
         state: directory
         owner: root
         mode: 0755
+
+    - name: Automated Zuul cluster reboots and updates
+      # Note this is run via cron because a zuul job can't run this playbook
+      # as the playbook relies on all jobs ending for graceful stops on the
+      # executors.
+      cron:
+        name: "Zuul cluster restart"
+        # Start Sundays at 00:01 UTC.
+        # Estimated completion time Sunday at 18:00 UTC.
+        minute: 1
+        hour: 0
+        weekday: 6
+        job: "flock -n /var/run/ansible/zuul_reboot.lock /usr/local/bin/ansible-playbook -f 20 /home/zuul/src/opendev.org/opendev/system-config/playbooks/zuul_reboot.yaml > /var/log/ansible/zuul_reboot.log 2>&1"
+
+    - name: Rotate Zuul restart logs
+      include_role:
+        name: logrotate
+      vars:
+        logrotate_file_name: /var/log/ansible/zuul_reboot.log
+        logrotate_frequency: weekly

playbooks/zuul_reboot.yaml

@@ -1,4 +1,5 @@
-# TODO We need to add a locking/failsafe check mechanism
+# This relies on flock -n /var/run/ansible/zuul_reboot.lock to ensure
+# we don't run multiple copies of this playbook concurrently.
 
 # TODO: stop pulling in the hourly job if we do this
 - name: "Ensure we are going to restart/reboot on the same image"