Bug 19403: Prevent Circulation.t to fail randomly

Bug 19403: Prevent Circulation.t to fail randomly

Due to the number of test cases handle by CanBookBeIssued, Circulation.t
fails randomly. To prevent that it is better to set some values.
For instance if the patron is a statistical patron (category_type=X),
the subroutine will return a STATS flag.

This patch also adds a subroutine to the test file to display the keys
of $error, $question and $alert set by CanBookBeIssued.
It will be easier to track other random failures.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>