fix: Displayed remote actor errors better

Author: kumar303

src/firefox/remote.js

@@ -54,7 +54,8 @@ export class RemoteFirefox {
           {to: addon.actor, type: request}, (response) => {
         if (response.error) {
           reject(
-            new WebExtError(`${request} response error: ${response.error}`));
+            new WebExtError(`${request} response error: ` +
+                            `${response.error}: ${response.message}`));
         } else {
           resolve(response);
         }

tests/test-firefox/test.remote.js

@@ -101,7 +101,10 @@ describe('firefox.remote', () => {
       it('throws when add-on actor requests fail', () => {
         const addon = fakeAddon();
         const client = fakeFirefoxClient({
-          makeRequestError: 'some actor request failure',
+          makeRequestError: {
+            error: 'unknownError',
+            message: 'some actor failure',
+          },
         });
 
         const conn = makeInstance(client);
@@ -110,7 +113,7 @@ describe('firefox.remote', () => {
           .catch(onlyInstancesOf(WebExtError, (error) => {
             assert.equal(
               error.message,
-              'requestTypes response error: some actor request failure');
+              'requestTypes response error: unknownError: some actor failure');
           }));
       });
     });