[SMT-COMP] Print non-(un)sat output to stderr (#2019)

[SMT-COMP] Print non-(un)sat output to stderr (#2019)

In the SMT-COMP runscript, we are currently discarding output on stdout
that is not "sat" or "unsat" when using `trywith` (this is not the case
with `finishwith`). Due to this, our tests might miss cases where CVC4
fails and prints an error on stdout when using `trywith`. This commit
changes the script to print output other than "sat" or "unsat" to
stderr.