kea v4 returns status-get 0 when not connected to database

During the missing lease database connection process, we send 'status-'get' to Kea. Kea v6 returns:

  {
    "result": 1,
    "text": "Error during command processing: no current lease manager is available"
  }

Kea v4 returns normal status:

  {
    "arguments": {
      "multi-threading-enabled": true,
      (...)
      "uptime": 4
    },
    "result": 0
  }

Getting result 0 on kea4 is misleading when there is no database connection.

These features should be included in tests tests/dhcp/test_database.py::test_db_retry*. Please inform QA about the merging solution for this issue.