Use lower case for onu variable in Berlin xgspon-zyxel-DT

* The tests expect the `onu` variable to have the vendor-specific part
  of the serial number is lower case.

Change-Id: I7c51786b6401d7b79b83410480a455759ef866e0
Signed-off-by: Cristina de Francisco <cristina.defrancisco@bisdn.de>
diff --git a/deployment-configs/berlin-community-pod-2-xgspon-zyxel-DT.yaml b/deployment-configs/berlin-community-pod-2-xgspon-zyxel-DT.yaml
index 76b4726..de31def 100644
--- a/deployment-configs/berlin-community-pod-2-xgspon-zyxel-DT.yaml
+++ b/deployment-configs/berlin-community-pod-2-xgspon-zyxel-DT.yaml
@@ -70,7 +70,7 @@
         dp_iface_name: eth1.7
         container_type: LXC
         container_name: ZYXE8CABE30B
-        onu: ZYXE8CABE30B
+        onu: ZYXE8cabe30b
         olt: S210Z14009247
         c_tag: 7
         s_tag: 41