Fixes #4973: Windows and Andoid: failsafe.cf in initial-promises doesn't...

... have a "execDate" variable, causing all reports to not contain the date/time
both /bin/date --rfc-3339=second and \"${g.rudder_sbin}\getDate.bat\" work on cygwin, so it's not a real problem
Merging, but it would be better if it were cleaner