engine: Minor changes in noVNC

This patch changes two things:
 - fixes the description of WebSocketProxy in the db upgrade script
 - derive protocol type of noVNC page from the currently served page.

Change-Id: Id9fdc22097aefee0ac13c0ff939269b66c526b86
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>