replace hard coded value for return value file by a ProgramJob class variable

according to new ProgramJob API
add file in results only if size > 0

results files are added to Job as results only if their size is > 0
the end_of job is not compute on datime.now but on the last time of
modification of job return value file.
if this file does not exist the fall back is still now.
fix status_actor.getresults if data size == 0 the size was false and
finally add to DB
dd output_type propertise for stdout and stderr parameter to avoid to
havbe thes parameter twice in ProgramJob