VOL-1190 Filter out unreachable device before reporting to ONOS

calling ListReachableLogicalDevices instead of ListLogicalDevices. The filtering is done in the voltha core

Change-Id: I517f963423b83c49bce1469ebb016af1eb72a4a9
diff --git a/ofagent/grpc_client.py b/ofagent/grpc_client.py
index 56af949..ab9417b 100644
--- a/ofagent/grpc_client.py
+++ b/ofagent/grpc_client.py
@@ -241,6 +241,13 @@
         returnValue(res.items)
 
     @inlineCallbacks
+    def list_reachable_logical_devices(self):
+        res = yield threads.deferToThread(
+            self.local_stub.ListReachableLogicalDevices, empty_pb2.Empty(),
+            timeout=self.grpc_timeout)
+        returnValue(res.items)
+
+    @inlineCallbacks
     def subscribe(self, subscriber):
         res = yield threads.deferToThread(
             self.local_stub.Subscribe, subscriber, timeout=self.grpc_timeout)