Test script documentation fixup

This commit provides a scriptable headline for the octal dump output.
When the received output of a test is empty or only whitespace, this
commit makes it clear that the octal dump putput is not the expected
output.

test/lib.sh

@@ -201,6 +201,7 @@ err(){
       echo "Received: $2"
   fi
   echo -e "\e[0m"
+  echo "Diff between Expected and Received:"
   echo "$ret"| od -t c > $dir/clixon-ret
   echo "$expect"| od -t c > $dir/clixon-expect
   diff $dir/clixon-expect $dir/clixon-ret