Log errors when resolving openID tokens in web api.

https://github.com/matrix-org/mjolnir/issues/416.

src/appservice/Api.ts

@@ -28,6 +28,7 @@ export class Api {
                 qs: { access_token: accessToken },
             }, (err, homeserver_response, body) => {
                 if (err) {
+                    console.error(`Error resolving openID token from ${this.homeserver}`, err);
                     reject(null);
                 }
 
@@ -35,6 +36,7 @@ export class Api {
                 try {
                     response = JSON.parse(body);
                 } catch (e) {
+                    console.error(`Received ill formed response from ${this.homeserver} when resolving an openID token`, e);
                     reject(null);
                     return;
                 }