Write to /etc/ssh with super user privileges

Not sure why it's working in CI or in the general case, but I've seen
this task fail with "Destination /etc/ssh not writable" from time to
time. This commit ensures it's always run with super user privilege so
it can write it /etc/ssh directory.

Change-Id: Ia753b5e842c20c21714111c6267ef70d53d9de4a

roles/tripleo-ssh-known-hosts/tasks/main.yml

@@ -1,6 +1,7 @@
 ---
 
 - name: Template /etc/ssh/ssh_known_hosts
+  become: true
   template:
     src: ssh_known_hosts.j2
     dest: /etc/ssh/ssh_known_hosts