Make virsh -d check its input

it was using atoi direct without checking leading to confusion
in case of flag error for example with -c

* tools/virsh.c: vshParseArgv() use virStrToLong_i and remove the
  unchecked atoi used to parse teh parameter

tools/virsh.c

@@ -11021,7 +11021,10 @@ vshParseArgv(vshControl *ctl, int argc, char **argv)
     while ((arg = getopt_long(end, argv, "d:hqtc:vrl:", opt, &idx)) != -1) {
         switch (arg) {
         case 'd':
-            ctl->debug = atoi(optarg);
+            if (virStrToLong_i(optarg, NULL, 10, &ctl->debug) < 0) {
+                vshError(ctl, _("option -d takes a numeric argument"), arg);
+                exit(EXIT_FAILURE);
+            }
             break;
         case 'h':
             help = 1;