Added read replica support

moto/rds2/models.py

@@ -88,14 +88,12 @@ class Database(object):
     def address(self):
         return "{0}.aaaaaaaaaa.{1}.rds.amazonaws.com".format(self.db_instance_identifier, self.region)
 
-    # TODO: confirm how this should represent in the RESULT JSON
     def add_replica(self, replica):
         self.replicas.append(replica.db_instance_identifier)
 
     def remove_replica(self, replica):
         self.replicas.remove(replica.db_instance_identifier)
 
-    # TODO: confirm how this should represent in the RESULT JSON
     def set_as_replica(self):
         self.is_replica = True
         self.replicas = []
@@ -210,7 +208,11 @@ class Database(object):
             "{{ replica }}"
         {%- endfor -%}
         ],
+        {%- if database.source_db_identifier -%}
+        "ReadReplicaSourceDBInstanceIdentifier": "{{ database.source_db_identifier }}",
+        {%- else -%}
         "ReadReplicaSourceDBInstanceIdentifier": null,
+        {%- endif -%}
         "SecondaryAvailabilityZone": null,
         "StatusInfos": null,
         "VpcSecurityGroups": [