[FIX] point_of_sale: test pos_basic_order do not actually jump in the backend

We avoid to actually jump in the back-end, to prevent
phantomjs to send requests to the server without waiting for them.

Indeed, clicking on the close & confirm button jumps ine the backend,
but the tour is actually finished (and succeeded) once these buttons
are clicked, and just clicked. The test does not actually check if these buttons
makes the user come back in the backend, and it does not wait
for the requests sent because of the jump in the backend to be completed.
Besides, the jump in the backend triggers the compilation
of the common and backend assets, which take some time.

These requests for which phantomjs does not wait triggers
the method `def _wait_remaining_requests(self)` in the
class `class HttpCase(TransactionCase)`, which
leads to the ugly tracebacks in the runbot, waiting
for the requests triggered by phantomjs to be finished.