Description of problem:
while it is true that we do state that an undercloud upgrade should be performed before making a minor update for the overcloud, it makes sense to have ansible-pacemaker pulled in from the start (think installation with all the latest packages, it makes no sense to demand an undercloud upgrade in this context).

This has been fixed upstream via:
https://review.rdoproject.org/r/#/c/15684/ (queens)
https://review.rdoproject.org/r/#/c/15957/ (pike)

If you do not have ansible-pacemaker on the undercloud you will hit these errors during a minor update:
u'TASK [include]
*****************************************************************',
 u'Thursday 09 August 2018  06:55:47 -0400 (0:00:00.388)
 0:00:10.970 ******* ',
  u'fatal: [controller-2]: FAILED! => {"failed": true, "reason": "no
  action detected in task. This often indicates a misspelled module
  name, or incorrect module path.\\n\\nThe error appears to have been in
  \'/var/lib/mistral/dd74d929-9322-44ba-817a-e6e2a4792169/Controller/update_tasks.yaml\':
  line 83, column 5, but may\\nbe elsewhere in the file depending on the
  exact syntax problem.\\n\\nThe offending line appears to be:\\n\\n
  register: haproxy_cert_mounted\\n  - name: Disable the haproxy cluster
  resource\\n    ^ here\\n\\n\\nThe error appears to have been in
  \'/var/lib/mistral/dd74d929-9322-44ba-817a-e6e2a4792169/Controller/update_tasks.yaml\':
  line 83, column 5, but may\\nbe elsewhere in the file depending on the
  exact syntax problem.\\n\\nThe offending line appears to be:\\n\\n
  register: haproxy_cert_mounted\\n  - name: Disable the haproxy cluster
  resource\\n    ^ here\\n\\nexception type: <class
  \'ansible.errors.AnsibleParserError\'>\\nexception: no action detected
  in task. This often indicates a misspelled module name, or incorrect
  module path.\\n\\nThe error appears to have been in
  \'/var/lib/mistral/dd74d929-9322-44ba-817a-e6e2a4792169/Controller/update_tasks.yaml\':
  line 83, column 5, but may\\nbe elsewhere in the file depending on the
  exact syntax problem.\\n\\nThe offending line appears to be:\\n\\n
  register: haproxy_cert_mounted\\n  - name: Disable the haproxy cluster
  resource\\n    ^ here\\n"}',
   u'',