Fix cookie tests

* Since a guider is not actually shown in setTourCookie (wasShown is
  false), the first article ID/page name can not be initialized yet,
  even if stickToFirstPage is used.  Thus, there is no need to load
  the tour spec here.

* Cast step to number when serializing cookie, and test this.

* Update cookie tests for new format, and check that the cookie can
  store more than one tour.

* Fix log comment about invalid JSON.

Change-Id: I783a82cbb7421f5f53a79c8fd56eb27c01b68169