Mass-edit massif tests to use unique output names

This just mass-substitutes massif.out -> massif.TESTNAME.out in all
vgtest and exp files, like so:

  for f in *.vgtest; do
    b=${f%.vgtest}
    perl -i -pe "s{massif\.out}{massif.$b.out}g" $f $b.*.exp*
  done
Much prettier output format in threaded mode