set the embargo on all the documents of a given record. @param date_file: the file from which to read the embargo end date. @param date_format: the format in which the date in L{date_file} is expected to be found. (default C{%Y-%m-%d}) @note: this function should be used after any file that need to be added to a record has been added, that is after any call to e.g. L{Move_Files_to_Storage} @note: This function expect C{sysno} to exist and be set to the current record. (that means it should be called after L{Get_Recid} or L{Create_Recid})