Fix mock PAM config on arm-packager machines

Checks for packager group must be early, before prompting user for
root password.

playbooks/groups/arm-packager.yml

@@ -35,6 +35,7 @@
 
   - name: allow packagers to use mock
     lineinfile: dest=/etc/pam.d/mock line="{{ item }} sufficient pam_succeed_if.so user ingroup packager use_uid quiet"
+    insertbefore: BOF
     with_items:
     - account
     - auth