Make id required for cluser-devices command

    - Fix for ONOS-997

Change-Id: I9becb74a44509d804404e8f8beb44ef718d0b9b6
diff --git a/cli/src/main/java/org/onosproject/cli/net/ClusterDevicesCommand.java b/cli/src/main/java/org/onosproject/cli/net/ClusterDevicesCommand.java
index bfd79b2..11b0f17 100644
--- a/cli/src/main/java/org/onosproject/cli/net/ClusterDevicesCommand.java
+++ b/cli/src/main/java/org/onosproject/cli/net/ClusterDevicesCommand.java
@@ -37,7 +37,7 @@
 public class ClusterDevicesCommand extends ClustersListCommand {
 
     @Argument(index = 0, name = "id", description = "Cluster ID",
-              required = false, multiValued = false)
+              required = true, multiValued = false)
     String id = null;
 
     @Override