Fixes #5503 : correct evaluation of promises by cfengine, to be able to delete file based on date

Based on https://github.com/vohi/core/commit/77caac16aab82cb8b6239d59cf5e5eae8bb7e853#diff-823bcdb0d3f3367a25567abbe6c3d973R288.patch , see also https://dev.cfengine.com/issues/6577
Related bug are 
- http://www.rudder-project.org/redmine/issues/5503
- http://www.rudder-project.org/redmine/issues/5565