Adjust settings so we can change the comments service URL from Django config

lms/envs/aws.py

@@ -60,3 +60,5 @@ XQUEUE_INTERFACE = AUTH_TOKENS['XQUEUE_INTERFACE']
 if 'COURSE_ID' in ENV_TOKENS:
     ASKBOT_URL = "courses/{0}/discussions/".format(ENV_TOKENS['COURSE_ID'])
 
+COMMENTS_SERVICE_URL = ENV_TOKENS["COMMENTS_SERVICE_URL"]
+

lms/lib/comment_client/settings.py

-SERVICE_HOST = 'http://localhost:4567'
+from django.conf import settings
+
+if hasattr(settings, "COMMENTS_SERVICE_URL"):
+    SERVICE_HOST = settings.COMMENTS_SERVICE_URL
+else:
+    SERVICE_HOST = 'http://localhost:4567'
 
 PREFIX = SERVICE_HOST + '/api/v1'