contrib/jenkins: Enable parallel make in make distcheck

Change-Id: Id7d4e6682be1d4f77979e896089b42f35548ca98
Related: OS#4421

contrib/jenkins.sh

@@ -54,11 +54,11 @@ cd "$base"
 autoreconf --install --force
 ./configure --enable-sanitize --enable-werror $GTP $CONFIG
 $MAKE $PARALLEL_MAKE
-DISTCHECK_CONFIGURE_FLAGS="$CONFIG" $MAKE distcheck
+DISTCHECK_CONFIGURE_FLAGS="$CONFIG" $MAKE $PARALLEL_MAKE distcheck
 
 if [ "$WITH_MANUALS" = "1" ] && [ "$PUBLISH" = "1" ]; then
 	make -C "$base/doc/manuals" publish
 fi
 
-$MAKE maintainer-clean
+$MAKE $PARALLEL_MAKE maintainer-clean
 osmo-clean-workspace.sh