ensure-docker: prevent issue on centos-7 where the socket does not exists

This change mitigate an issue introduced by
https://review.opendev.org/c/zuul/zuul-jobs/+/787271

Fixes: https://bugs.launchpad.net/tripleo/+bug/1925372
Change-Id: I49f527b1c8a16e0b9f1718f23a960733003909ca

roles/ensure-docker/handlers/main.yaml

@@ -6,6 +6,7 @@
     enabled: yes
     state: stopped
   listen: Restart docker
+  failed_when: false
 
 - name: Assure docker service is running
   become: true
@@ -22,6 +23,7 @@
     enabled: yes
     state: started
   listen: Restart docker
+  failed_when: false
 
 - name: Correct group ownership on docker sock
   become: true