Merge pull request #899 from MetaMask/i893-DenodeifyKeyringController

Fix incorrect nodeification and add descriptive error to help find in future

app/scripts/keyring-controller.js

@@ -282,7 +282,7 @@ module.exports = class KeyringController extends EventEmitter {
   setSelectedAccount (address) {
     var addr = normalize(address)
     this.configManager.setSelectedAccount(addr)
-    Promise.resolve(addr)
+    return Promise.resolve(addr)
   }
 
   // Save Account Label

app/scripts/lib/nodeify.js

@@ -6,12 +6,19 @@ module.exports = function (promiseFn) {
     }
     var cb = arguments[arguments.length - 1]
 
-    return promiseFn.apply(this, args)
-    .then(function (result) {
+    const nodeified = promiseFn.apply(this, args)
+
+    if (!nodeified) {
+      const methodName = String(promiseFn).split('(')[0]
+      throw new Error(`The ${methodName} did not return a Promise, but was nodeified.`)
+    }
+    nodeified.then(function (result) {
       cb(null, result)
     })
     .catch(function (reason) {
       cb(reason)
     })
+
+    return nodeified
   }
 }