Enable download-api-helper to be started for existing user

tests/js/download-api-helper.js

@@ -2,33 +2,49 @@
 This script creates 3 new objects into a new realm. These are objects are validated to exists by the download api tests.
 */
 'use strict';
-
+console.log("download-api-helper started");
 const username = process.argv[2];
 const realmName = process.argv[3];
 const realmModule = process.argv[4];
 
 var Realm = require(realmModule);
-Realm.Sync.User.register('http://localhost:9080', username, 'password', (error, user) => {
+
+function createObjects(user) {
+    const config = {
+        sync: { user, 
+            url: `realm://localhost:9080/~/${realmName}`, 
+            error: err => console.log(err) 
+        },
+        schema: [{ name: 'Dog', properties: { name: 'string' } }]
+    };
+
+    var realm = new Realm(config);
+
+    realm.write(() => {
+        for (let i = 1; i <= 3; i++) {
+            realm.create('Dog', { name: `Lassy ${i}` });
+        }
+    });
+
+    console.log("Dogs count " + realm.objects('Dog').length);
+    setTimeout(() => process.exit(0), 3000);
+}
+
+Realm.Sync.User.register('http://localhost:9080', username, 'password', (error, registeredUser) => {
     if (error) {
-        console.log(error);
-        process.exit(-2);
-    } else {
-        const config = {
-            sync: { user, url: `realm://localhost:9080/~/${realmName}`, error: err => console.log(err) },
-            schema: [{ name: 'Dog', properties: { name: 'string' } }]
-        };
-
-        var realm = new Realm(config);
-
-        realm.write(() => {
-            for (let i = 1; i <= 3; i++) {
-                realm.create('Dog', { name: `Lassy ${i}` });
+        const registrationError = JSON.stringify(error);
+        Realm.Sync.User.login('http://localhost:9080', username, 'password', (err, loggedUser) => {
+            if (err) {
+                const loginError = JSON.stringify(err);
+                console.error("download-api-helper failed:\n User.register() error:\n" + registrationError + "\n User.login() error:\n" + loginError);
+                process.exit(-2);
+            }
+            else {
+                createObjects(loggedUser);
             }
         });
-
-        console.log("Dogs count " + realm.objects('Dog').length);
-        setTimeout(() => process.exit(0), 3000);
+    } 
+    else {    
+        createObjects(registeredUser);
     }
-});
-
-
+});