Use the current HS for guest login

Make sure that we use the homeserver from localstorage for guest regsistration,
in preference to the default.

Also rename the parameters for loadSession

src/components/structures/MatrixChat.js

@@ -173,8 +173,8 @@ module.exports = React.createClass({
         Lifecycle.loadSession({
             queryParams: this.props.startingQueryParams,
             enableGuest: this.props.enableGuest,
-            hsUrl: this.getDefaultHsUrl(),
-            isUrl: this.getDefaultIsUrl(),
+            guestHsUrl: this.getCurrentHsUrl(),
+            guestIsUrl: this.getCurrentIsUrl(),
         }).done(()=>{
             // stuff this through the dispatcher so that it happens
             // after the on_logged_in action.