haproxy supports websocket by default everywhere, so reuse this and make
type=websocket only needed if some specific configuration like
websocket-path-list or websocket-transparent have to be set.

As a result of implementing this feature X-Forwarded-Proto and
X-Forwarded-Port header support is now enabled per slave and not just
globally.

X-Real-Ip is only available for websocket paths, previous implementation
was simply wrong, and this has been fixed and asserted in tests.

Tests have been slightly updated to make it easier to follow the real
websocket logic.