services/cluster/vkube: update any app
services/cluster/vkube: update any app

Allow 'vkube update' to update apps that don't use cluster-agent
and pod-agent. This means that it can be used to perform a rolling
update on any replication controller that has an 'application' label.

Change-Id: Ie8bc5d4e9f4d9ee02dd6589c4707ee6bdbe8651d

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref