MEDIUM: startup: 'haproxy -c' is quiet when valid

MODE_CHECK does not output "Configuration file is valid" by default
anymore. To display this message the -V option must be used with -c.

However the warning and errors are still output by default if they
exist.

This allows to clean the output of the systemd unit file with is doing a
-c.

src/haproxy.c

@@ -2375,6 +2375,7 @@ static void init(int argc, char **argv)
 
 		if (pr || px) {
 			/* At least one peer or one listener has been found */
+			if (global.mode & MODE_VERBOSE)
 				qfprintf(stdout, "Configuration file is valid\n");
 			deinit_and_exit(0);
 		}