BF: job_templates: Call tar with --ignore-failed-read

After a command completes, it writes to "status.$subjob".  If, after
completing its command, a subjob sees that the status files for all
the other subjobs are in, it claims responsibility for the
post-processing step.  For the datalad-run orchestrators,
post-processing includes calling `find` to get a list of newly added
files and then calling `tar` with these files as input.

Given that the above procedure waits until each command exits, the
hope is that all the output files are created and any temporary files
will have been cleaned up.  But we're hitting into cases [*] where
apparently intermediate files are present for the `find` call but gone
by the time `tar` is called.  This leads to `tar` exiting with a
non-zero status and the post-processing being aborted.

Until someone has a better idea of how to deal with this, instruct
`tar` to exit with zero even if an expected file isn't present.  This
allows post-processing to succeed and the incident will still show up
in the captured stderr.

[*] ReproNim#438 (comment)

Author: kyleam

reproman/support/jobs/job_templates/runscript/includes/post-run.template.sh

@@ -29,5 +29,6 @@ mkdir -p "$rootdir/outputs"
 tar \
   -C "$workdir" \
   --files-from "$metadir/togethome" \
+  --ignore-failed-read \
   -cz \
   -f "$rootdir/outputs/$jobid.tar.gz"