buildbot: run spec.py explicitly with python2

buildbot/runspec.sh

@@ -20,7 +20,7 @@ RESDIR="/ben/firm/public_html/nightly_spec_results/${TARGET_TRIPLE}"
 mkdir -p "${RESDIR}" || dir "Couldn't setup result dir"
 ln -sf "${RESDIR}" result || die "Couldn't setup result dir"
 
-${MYDIR}/../spec.py --config-only $SPEC_PY_FLAGS > config/default.cfg
+python2 ${MYDIR}/../spec.py --config-only $SPEC_PY_FLAGS > config/default.cfg
 (set +eu ; . shrc && eval $RUN_SCRIPT | tee log.txt)
 
 # Error handling