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.

test/lib/plugin.js

@@ -66,8 +66,8 @@ describe("lib/plugin", function() {
 			await controllerPlugin.onInstanceConfigFieldChanged({}, {}, "foo", null);
 			await controllerPlugin.onMetrics();
 			await controllerPlugin.onShutdown();
-			controllerPlugin.onSlaveConnectionEvent({}, "connect");
-			await controllerPlugin.onPrepareSlaveDisconnect({});
+			controllerPlugin.onHostConnectionEvent({}, "connect");
+			await controllerPlugin.onPrepareHostDisconnect({});
 		});
 	});