VOL-1049 OpenOLT - logical port not found handling

Change-Id: I9ef00883224d7390467fffe181fcb9ff372949e4
diff --git a/voltha/adapters/openolt/openolt_device.py b/voltha/adapters/openolt/openolt_device.py
index 8921761..7b3e272 100644
--- a/voltha/adapters/openolt/openolt_device.py
+++ b/voltha/adapters/openolt/openolt_device.py
@@ -757,8 +757,13 @@
     def update_logical_port_stats(self, port_stats):
         # FIXME
         label = 'nni-{}'.format(port_stats.intf_id)
-        logical_port = self.adapter_agent.get_logical_port(
-            self.logical_device_id, label)
+        try:
+            logical_port = self.adapter_agent.get_logical_port(
+                self.logical_device_id, label)
+        except KeyError as e:
+            self.log.warn('logical port was not found, it may not have been '
+                          'created yet', exception=e)
+            logical_port = None
 
         if logical_port is None:
             self.log.error('logical-port-is-None',