scripts: Always convert result to resolved Promise

As discovered in 18F#51, the
`UnhandledPromiseRejectionWarning` and `PromiseRejectionHandledWarning`
warnings were apparently added in v6.6.0
(https://nodejs.org/en/blog/release/v6.6.0/); specifically it was added
by nodejs/node#8223. See also:

  nodejs/node#6439
  nodejs/node#8217
  https://nodejs.org/dist/latest-v6.x/docs/api/process.html#process_event_unhandledrejection
  https://nodejs.org/dist/latest-v6.x/docs/api/process.html#process_event_rejectionhandled
  https://nodejs.org/dist/latest-v6.x/docs/api/process.html#process_event_warning

Test failures from `test/integration-test.js` after upgrading to Node
v6.9.1 showed extra output such as:

```
  (node:39696) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): null
  (node:39696) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 2)
```

This was happening because `scripts/slack-github-issues.js` created a
Hubot listener that returned a `Promise` so that the integration test
could use `.should.be.rejectedWith` assertions. Rather than jump through
hoops to quash the warnings, this change now causes the listener's
`catch` handler to return the result of the rejected `Promise`,
converting it to a fulfilled `Promise` in the process.

Since Hubot never used the result anyway, the only effect it has in
production is to eliminate the warning messages. The tests now just
check that the `Promise` returned by the listener callback is fulfilled
with the expected error result, with practically no loss in clarity.

scripts/slack-github-issues.js

@@ -42,10 +42,13 @@ function fileIssue(filer, response) {
       return issueUrl;
     })
     .catch(function(err) {
+      var result = err;
+
       if (err) {
-        response.reply(err.message || err);
+        result = err.message || err;
+        response.reply(result);
       }
-      return Promise.reject(err);
+      return result;
     });
 }
 

test/integration-test.js

@@ -26,7 +26,7 @@ chai.should();
 chai.use(chaiAsPromised);
 
 describe('Integration test', function() {
-  var room, listenerCallbackPromise, logHelper, apiStubServer, config,
+  var room, listenerResult, logHelper, apiStubServer, config,
       apiServerDefaults, reactionAddedMessage, patchReactMethodOntoRoom,
       patchListenerCallbackAndImpl, sendReaction, initLogMessages,
       wrapInfoMessages, matchingRule = 'reactionName: evergreen_tree, ' +
@@ -158,7 +158,7 @@ describe('Integration test', function() {
     });
 
     listener.callback = function(response) {
-      listenerCallbackPromise = callback(response);
+      listenerResult = callback(response);
     };
   };
 
@@ -179,7 +179,7 @@ describe('Integration test', function() {
   sendReaction = function(reactionName) {
     logHelper.beginCapture();
     return room.user.react('mbland', reactionName)
-      .then(function() { return listenerCallbackPromise; })
+      .then(function() { return listenerResult; })
       .then(helpers.resolveNextTick, helpers.rejectNextTick)
       .then(logHelper.endCaptureResolve(), logHelper.endCaptureReject());
   };
@@ -240,8 +240,8 @@ describe('Integration test', function() {
 
     response.statusCode = 500;
     response.payload = payload;
-    return sendReaction(helpers.REACTION)
-      .should.be.rejectedWith(errorReply).then(function() {
+    return sendReaction(helpers.REACTION).should.become(errorReply)
+      .then(function() {
         var logMessages;
 
         room.messages.should.eql([
@@ -268,10 +268,9 @@ describe('Integration test', function() {
       response.payload = { message: 'should not happen' };
     });
 
-    return sendReaction('sad-face').should.be.rejectedWith(null)
-      .then(function() {
-        room.messages.should.eql([['mbland', 'sad-face']]);
-        logHelper.filteredMessages().should.eql(initLogMessages());
-      });
+    return sendReaction('sad-face').should.become(null).then(function() {
+      room.messages.should.eql([['mbland', 'sad-face']]);
+      logHelper.filteredMessages().should.eql(initLogMessages());
+    });
   });
 });