jobd.pl: touch ctime of lockfile on each run
The default location of the lock file is in /tmp. Some systems
periodically clean /tmp of old files (i.e. files that have not
been accessed, modified or status changed) periodically.
We do not want the lock file to be removed, so touch the ctime
to prevent this. The mtime will continue to reflect the time
jobd was started while the ctime will reflect the beginning of
the most recent run.
We do not bother with atime since on some systems changes to
atime may be completely ignored.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>