[ffwd3][update] Run OVN external update only once

The ovn_controller update tasks are in external_update but
reused by upgrade process. During the upgrade we run on
all hosts and not just undercloud causing the tasks to get
executed n times over so in case of 500 nodes we would end
up restarting ovn_controller 500 times.

This should be solved in upgrade by simply triggering only
on first controller.

The run_once would not work here due to tripleo_free strategy.

Change-Id: I04117dec68f0892ee59f0b997fb6eb0443218846
Resolves: rhbz#2229761

deployment/ovn/ovn-controller-container-puppet.yaml

@@ -658,7 +658,13 @@ outputs:
           until: async_poll_results.finished
           retries: {get_param: OVNControllerUpdateTimeout}
           delay: 1
-      upgrade_tasks: *ovn_controller_update
+      upgrade_tasks:
+        - name: set first_controller fact
+          set_fact:
+            first_controller: "{{ groups['ovn_controller']|first|lower == ansible_facts['hostname']|lower }}"
+        - name: Trigger external_update OVN block on first controller
+          when: first_controller | bool
+          block: *ovn_controller_update
       scale_tasks:
         - when:
             - step|int == 1