Synchronize request init in AbstractHttpSockJsSession

Although unlikely in practice (but not impossible), the SockJS
integration tests write a message while the request is initializing.
This change adds synchronization around request intiailization
for the SockJS HTTP sesion.

Issue: SPR-11916
Log name of test for WebSocket integration tests

This makes it easier to trace log output on the CI server where the
output is per class.