mysql-test/mysql-test-run.pl : Output the usage error if one is given....

mysql-test/mysql-test-run.pl  :  Output the usage error if one is given. (Found when fixing bug#20303)


mysql-test/mysql-test-run.pl:
  Found when fixing bug#20303: The "usage()" function ignored the message it was given,
  so we got no real indication about the problem. Print it if one is given.

mysql-test/mysql-test-run.pl

@@ -2459,6 +2459,13 @@ sub valgrind_arguments {
 ##############################################################################
 
 sub usage ($) {
+  my $message= shift;
+
+  if ( $message )
+  {
+    print STDERR "$message \n";
+  }
+
   print STDERR <<HERE;
 
 mysql-test-run [ OPTIONS ] [ TESTCASE ]