Adding serial_number information to OLTDevice

Change-Id: Ied682803092f0538cf5beaf59dcaeedd65be14c5
diff --git a/xos/synchronizer/pull_steps/pull_olts.py b/xos/synchronizer/pull_steps/pull_olts.py
index 0f3c199..6c57cde 100644
--- a/xos/synchronizer/pull_steps/pull_olts.py
+++ b/xos/synchronizer/pull_steps/pull_olts.py
@@ -129,6 +129,7 @@
             model.device_id = olt["id"]
             model.admin_state = olt["admin_state"]
             model.oper_status = olt["oper_status"]
+            model.serial_number = olt['serial_number']
 
             model.volt_service = self.volt_service
             model.volt_service_id = self.volt_service.id
diff --git a/xos/synchronizer/pull_steps/test_pull_olts.py b/xos/synchronizer/pull_steps/test_pull_olts.py
index fd09a1f..a06d3ff 100644
--- a/xos/synchronizer/pull_steps/test_pull_olts.py
+++ b/xos/synchronizer/pull_steps/test_pull_olts.py
@@ -89,7 +89,8 @@
                     "type": "simulated_olt",
                     "host_and_port": "172.17.0.1:50060",
                     "admin_state": "ENABLED",
-                    "oper_status": "ACTIVE"
+                    "oper_status": "ACTIVE",
+                    "serial_number": "serial_number",
                 }
             ]
         }