Update the job file on feedback

This is needed to convert waitforjobchanges to use inotify and the
on-disk version and decouple it from the job queue lock. No replication
to remote nodes is done, to keep the operation fast.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>