journalctl: use _COMM= match for scripts

In case of scripts, _EXE is set to the interpreter name, and
_COMM is set based on the file name. Add a match for _COMM,
and _EXE if the interpreter is not a link (e.g. for yum,
the interpreter is /usr/bin/python, but it is a link to
/usr/bin/python2, which in turn is a link to /usr/bin/python2.7,
at least on Fedora, so we end up with _EXE=/usr/bin/python2.7).
I don't think that such link chasing makes sense, because
the final _EXE name is more likely to change.