Bug 27947: (QA follow-up) Make parameters a hashref

Bug 27947: (QA follow-up) Make parameters a hashref

This patch makes the Koha::ArticleRequest->cancel parameters into a
hashref. (Missing) tests are added for those parameters being set as
well.

Calls to ->cancel are updated.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/ArticleRequest.t \
           t/db_dependent/api/v1/article_requests.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>