Make heartbeat url wait for courses to be loaded

lms/djangoapps/heartbeat/views.py

 import json
 from datetime import datetime
 from django.http import HttpResponse
+from xmodule.modulestore.django import modulestore
 
 
 def heartbeat(request):
@@ -8,6 +9,7 @@ def heartbeat(request):
     Simple view that a loadbalancer can check to verify that the app is up
     """
     output = {
-        'date': datetime.now().isoformat()
+        'date': datetime.now().isoformat(),
+        'courses': [course.location for course in modulestore().get_courses()],
     }
     return HttpResponse(json.dumps(output, indent=4))