contrib/jenkins: Enable parallel make in make distcheck

Change-Id: I8f112ed6de4b1b7c28fbb790fede0e1a387a4e22
Related: OS#4421
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index dca33bb..baeba59 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -71,12 +71,12 @@
   || cat-testlogs.sh
 LD_LIBRARY_PATH="$inst/lib" \
   DISTCHECK_CONFIGURE_FLAGS="$enable_werror --enable-smpp $IU --enable-external-tests $CONFIG" \
-  $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