Our own Janus WS client would create a single WS session and then create
all rooms under this one session and run all publishes and subscribers
under the same session. This is not a restiction imposed by Janus
though, which allows participation in one room by multiple sessions.
Remove this restriction to more closely mirror Janus behaviour.
Change-Id: Ic11f961369ce5ded599a7a22cd730236460a8c61