Fixed wrong scheme for secure websocket

Websocket server always constructed QWebSocketHandshakeRequest like for
non-secure socket without checking SecureMode. This led to the fact that
secure socket had "ws" scheme.

Task-number: QTBUG-55927
Change-Id: I881766f55182136072fd23f3fefe93ea60f3d27d
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>