Fix: resolve a set of exceptions raised by tempest integration test

Change-Id: I7931f969d93afc28819dff31e2857cfbc6f720ac
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/InstancePortManager.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/InstancePortManager.java
index 9878de0..3f204fb 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/InstancePortManager.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/InstancePortManager.java
@@ -146,6 +146,13 @@
         checkArgument(!Strings.isNullOrEmpty(instancePort.portId()),
                                                     ERR_NULL_INSTANCE_PORT_ID);
 
+        // in case OpenStack removes the port prior to OVS, we will not update
+        // the instance port as it does not exist in the store
+        if (instancePortStore.instancePort(instancePort.portId()) == null) {
+            log.warn("Unable to update instance port {}, as it does not exist", instancePort.portId());
+            return;
+        }
+
         instancePortStore.updateInstancePort(instancePort);
         log.info(String.format(MSG_INSTANCE_PORT, instancePort.portId(), MSG_UPDATED));
     }