mtr: fix the debug printout

to print all arguments of _verbose(), not just the number of them

Author: vuvova

mysql-test/lib/My/SafeProcess.pm

@@ -628,7 +628,7 @@ sub self2str {
 
 sub _verbose {
   return unless $_verbose;
-  print STDERR " ## ". @_. "\n";
+  print STDERR " ## @_\n";
 }