contrib/jenkins: Enable parallel make in make distcheck

Change-Id: I38f59aec482d3a8e2690913bc55728a96399659e
Related: OS#4421
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index ac7363e..46d38f7 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -60,12 +60,12 @@
 $MAKE $PARALLEL_MAKE
 $MAKE check \
   || cat-testlogs.sh
-$MAKE distcheck \
+$MAKE $PARALLEL_MAKE distcheck \
   || cat-testlogs.sh
 
 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