Fix do not return PROMISE_RESULT_CHANGE from vars and class actuators

This impacted repair status indirectly for methods, and thereby services.

Close #5273
PromiseResultUpdate, do not let SKIPPED override NOOP.
Factor out RenderTemplateCFEngine, RenderTemplateMustache
Only commit mustache template to disk if rendering is successful

Use Buffer instead of Writer for MustacheRender. Redmine #5292
Redmine#4848: fix peers, peerleader, and peerleaders functions and add tests