fix issue with IM that causes commandlines that are executed to be incorrect.

server-tools/instance-manager/instance.cc

@@ -181,6 +181,7 @@ static int start_process(Instance_options *instance_options,
   if (cmdline == NULL)
     return 1;
     
+  cmdline[0]= 0;
   for (int i= 0; instance_options->argv[i] != 0; i++)
   {
     strcat(cmdline, "\"");