Add: Acceptance tests for warn only and mustache templating

Modified by: Kristian Amlie <kristian.amlie@cfengine.com>
(cherry picked from commit b4c5f6fd9ff7209896eb3b46a96d22b92616186d)
support dry-run for mustache templates. Redmine #6739
(cherry picked from commit 8924c1e66f7a2e531e28462107e5a0ac431fa989)
tag mustace acceptance tests with story_id 5535
(cherry picked from commit 832691fb6041651651a6d0be200f5ad50cd33a1b)