Rename Slave to Host

The role of a slave as a host for Factorio servers is not well reflected
in its name and has caused confusion among users.  Rename slave to host
to better reflect its role as a host of Factorio servers.

plugins/player_auth/instance.js

@@ -18,7 +18,7 @@ class InstancePlugin extends libPlugin.BaseInstancePlugin {
 
 	async handleEvent(event) {
 		if (event.type === "open_dialog") {
-			if (!this.slave.connector.connected) {
+			if (!this.host.connector.connected) {
 				await this.sendRcon(`/web-login error ${event.player} login is temporarily unavailable`);
 				return;
 			}