Prevent JER/JEC cache status file updates from batch jobs

Configs should be tested locally, so this status file should usually be updated not too far before batch jobs are launched, but when there is an update in between several of them may try to update the file at the same time, or one might try to read it while another is writing a new version. One option is to lock it before writing (or force the update from the 'driver' task to reduce this probability).