tools: streamline exit codes, fix exit codes for vsubs

This should bring us closer to the exit codes now documented in
varnishd.rst

Fixes #1572 for tools

bin/varnishlog/varnishlog.c

@@ -82,7 +82,7 @@ openout(int append)
 	else
 		LOG.fo = fopen(LOG.w_arg, append ? "a" : "w");
 	if (LOG.fo == NULL)
-		VUT_Error(1, "Can't open output file (%s)",
+		VUT_Error(2, "Can't open output file (%s)",
 		    LOG.B_opt ? VSL_Error(VUT.vsl) : strerror(errno));
 	VUT.dispatch_priv = LOG.fo;
 }

lib/libvarnishtools/vut.c

@@ -159,7 +159,7 @@ VUT_Arg(int opt, const char *arg)
 	case 'V':
 		/* Print version number and exit */
 		VCS_Message(VUT.progname);
-		exit(1);
+		exit(0);
 	default:
 		AN(VUT.vsl);
 		i = VSL_Arg(VUT.vsl, opt, arg);