no websocket @Push in push-sample, security-sample-managed

[mz0]

Push works only over XHR, websocket is not "upgraded" - instead of 101 server sends 200.
Looks like vaadin/framework#8734 (comment)

2017-12-04 20:40:02.317 WARN 30238 --- [ XNIO-2 task-1] org.atmosphere.util.IOUtils : More than one Servlet Mapping defined. WebSocket may not work io.undertow.servlet.spec.ServletRegistrationImpl@..
2017-12-04 20:40:02.320 INFO 30238 --- [ XNIO-2 task-1] o.a.container.JSR356AsyncSupport : JSR 356 Mapping path /VAADIN

Updating Vaadin 8.0.2 to 8.1.7 has no effect.