Switch to 2 parallel run

src/main/resources/create-tarballs.sh

@@ -120,7 +120,10 @@ for (( i = 0 ; i < ${#TARBALLS[@]} ; i++ )); do
   fi
 done
 
-N=4
+# N is a parameter that describes the number of tarballs that are created in
+# parallel.
+
+N=2
 for (( i = 0 ; i < ${#TARBALLS[@]} ; i++ )); do
   ((j=j%N)); ((j++==0)) && wait
   {