Server panics when no config file is found

Can't do anything useful without config at this point, so we
might as well panic rather than confuse people. Minor cleanup of
config.

src/bin/grin.rs

@@ -378,10 +378,7 @@ fn server_command(server_args: Option<&ArgMatches>, mut global_config: GlobalCon
 				.chain_type,
 		);
 	} else {
-		info!(
-			LOGGER,
-			"Starting the Grin server (no configuration file) ..."
-		);
+		panic!("No configuration found.");
 	}
 
 	// just get defaults from the global config