tests: cucumber test certification is broken and not executed in CI

@HugoTrentesaux your test fail on master:

Feature: Certification
  Scenario: Dave certifies Alice
   ?  When dave certifies alice
   ?  Then alice should be certified by dave
  Scenario: Dave certifies Alice (but dave is not certified by charlie, this test should fail)
   ?  When dave certifies alice
   ?  Then dave should be certified by charlie
      Step failed: /home/elois/dev/duniter/duniter-v2s/end2end-tests/cucumber-features/certification.feature:13:9
      Captured output: 
      Step panicked. Captured output: no certification found from charlie to dave

We not catch that because this test is not executed on CI. Please fix this test then add it in the CI.