VOL-1774 Etcd Crash Handling

Change-Id: I1eeb726654c3972fd0a4fafae134607e5a810415
diff --git a/ro_core/core/grpc_nbi_api_handler.go b/ro_core/core/grpc_nbi_api_handler.go
index a611337..0a73ff2 100644
--- a/ro_core/core/grpc_nbi_api_handler.go
+++ b/ro_core/core/grpc_nbi_api_handler.go
@@ -153,7 +153,12 @@
 // ListDevices returns the contents of all devices known to the system
 func (handler *APIHandler) ListDevices(ctx context.Context, empty *empty.Empty) (*voltha.Devices, error) {
 	log.Debug("ListDevices")
-	return handler.deviceMgr.ListDevices()
+	devices, err := handler.deviceMgr.ListDevices()
+	if err != nil {
+		log.Errorw("failed-to-list-devices", log.Fields{"error": err})
+		return nil, err
+	}
+	return devices, nil
 }
 
 // ListDeviceIds returns the list of device ids managed by a voltha core