private Optional<Node> getNode(String hostname, ApplicationId application, @SuppressWarnings("unused") Mutex applicationLock) {
        return nodeRepository().nodes().node(hostname)
                               .filter(node -> node.state() == Node.State.active)
                               .filter(node -> node.allocation().isPresent())
                               .filter(node -> node.allocation().get().owner().equals(application));
    }
Get node by given hostname and application. The applicationLock must be held when calling this
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/NodeHealthTracker.java