Fixed failing tests after performing a merge.
Re #8578 - Edited conftest- tests from private_key_repository_test use unique database
Re #8578 - Repaired test after review- edited conftest - inicialization database before each test
Re #8578 - Remaked tests files- created tests for new functions - set_certificate_revoked, clear_certificate_revocation, get_all_revoked_by, get_all_issued_by