Bug 20612: Unit tests

Bug 20612: Unit tests

This patch makes the oauth.t tests leverage on the new Koha::ApiKey(s)
classes. It adds tests for expired tokens too.

To test:
- Apply this patch
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/oauth.t
=> FAIL: Tests should fail without the rest of the patches.

Sponsored-by: ByWater Solutions
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Benjamin Rokseth <benjamin.rokseth@deichman.no>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>