Respect dryrun in mustache templates

Redmine: https://dev.cfengine.com/issues/6739

Mustache now respects dry-run for
* body agent control, dryrun
* cf-agent --dry-run
* body action, with action_polcy => "warn"

Acceptance tests enabled and tagged.
PROMISE_RESULT_WARN instead of FAIL. That's what is mostly in use for existing ```DONTDO``` or ```cfa_warn``` cases.