Add serial_number to flex olt tosca

Change-Id: Iabb527937bf74391f8ea5a8fc241ee1d92897ee4
diff --git a/tosca-configs/att-workflow/flex-ocp-cord-voltha-master-olt.yaml b/tosca-configs/att-workflow/flex-ocp-cord-voltha-master-olt.yaml
index 43cdb3a..013cffc 100755
--- a/tosca-configs/att-workflow/flex-ocp-cord-voltha-master-olt.yaml
+++ b/tosca-configs/att-workflow/flex-ocp-cord-voltha-master-olt.yaml
@@ -42,6 +42,7 @@
         outer_tpid: "0x8100"
         uplink: "65536"
         nas_id: "NAS_ID"
+        serial_number: "EC1838000853"
       requirements:
         - volt_service:
             node: service#volt