Scenario:
Try to create Tsigkey using empty string

Actual Result:
Tsigkey is successfully created
2021-06-27 15:59:29.035 292921 INFO tempest.lib.common.rest_client [req-7e103208-0473-40ea-a040-0d6cf5bb7a61 ] Request (TsigkeyAdminTest:test_create_tsigkey_for_zone_empty_secret): 201 POST http://10.35.64.8/dns/v2/tsigkeys 0.090s
2021-06-27 15:59:29.036 292921 DEBUG tempest.lib.common.rest_client [req-7e103208-0473-40ea-a040-0d6cf5bb7a61 ] Request - Headers: {'Content-Type': 'application/json', 'Accept': 'application/json', 'X-Auth-Token': '<omitted>'}
        Body: {"name": "Example_Key-1226165891.com.", "algorithm": "hmac-sha256", "secret": "", "scope": "ZONE", "resource_id": "78ad8add-35ee-4bfe-9835-50dccf0fc807"}
    Response - Headers: {'date': 'Sun, 27 Jun 2021 12:59:28 GMT', 'server': 'Apache/2.4.41 (Ubuntu)', 'location': 'http://10.35.64.8/dns/v2/tsigkeys/f989a5c9-efe7-4cfd-b15e-38d91543e3ea', 'content-length': '356', 'x-openstack-request-id': 'req-7e103208-0473-40ea-a040-0d6cf5bb7a61', 'connection': 'close', 'content-type': 'application/json', 'status': '201', 'content-location': 'http://10.35.64.8/dns/v2/tsigkeys'}
        Body: b'{"id": "f989a5c9-efe7-4cfd-b15e-38d91543e3ea", "name": "Example_Key-1226165891.com.", "algorithm": "hmac-sha256", "secret": "", "scope": "ZONE", "resource_id": "78ad8add-35ee-4bfe-9835-50dccf0fc807", "created_at": "2021-06-27T12:59:29.000000", "updated_at": null, "links": {"self": "http://10.35.64.8/dns/v2/tsigkeys/f989a5c9-efe7-4cfd-b15e-38d91543e3ea"}}' _log_request_full /opt/stack/tempest/tempest/lib/common/rest_client.py:450
2021-06-27 15:59:29.100 292921 INFO tempest.lib.common.rest_client [req-47cf30b1-68ca-454b-b9e8-1c0f3cfade34 ] Request (TsigkeyAdminTest:_run_cleanups): 202 DELETE http://10.35.64.8/dns/v2/zones/78ad8add-35ee-4bfe-9835-50dccf0fc807 0.062s
2021-06-27 15:59:29.100 292921 DEBUG tempest.lib.common.rest_client [req-47cf30b1-68ca-454b-b9e8-1c0f3cfade34 ] Request - Headers: {'Content-Type': 'application/json', 'Accept': 'application/json', 'X-Auth-Token': '<omitted>'}

Expected:
Tsigkey should fail to be created