Add smoke tests for generated GAPICs

[parthea]

See links to handwritten smoke / system test in autogenerated clients such as the one for google/cloud/bigquery/connection. Ideally we would autogenerate these tests rather than manually maintaining them

Here is a list of all handwritten smoke tests, in case it helps if we decide to create an automated smoke test:

• https://github.com/googleapis/python-bigquery-connection/blob/2afc697f17335a6378abac8563b75e562bbfa5cc/tests/system.py#L30-L36
• https://github.com/googleapis/python-bigquery-datatransfer/blob/091adac922eae2d5b35816f6dc07913a594bd169/tests/system.py#L29-L36
• https://github.com/googleapis/python-bigquery-reservation/blob/1fd7e69a0eeb98de9fd3092247eb9d06147cbad6/tests/system.py#L29-L36
• https://github.com/googleapis/python-container/blob/96ddca67bf0e23c9c8fb838ebdfb000bee7d1b02/tests/system/gapic/v1/test_system_cluster_manager_v1.py#L21-L28
• https://github.com/googleapis/python-dataproc/blob/cbae95825665314081aaab38166600e33e6275d8/tests/system/gapic/v1/test_system_cluster_controller_v1.py#L25-L34
• https://github.com/googleapis/python-dlp/blob/966ef5808209c7d283426898c3ad79ac6bf52194/tests/system/gapic/v2/test_system_dlp_service_v2.py#L21-L41
• https://github.com/googleapis/python-kms/blob/0a09d118e680e4d90df6df65548bc5740952df2d/tests/system/test_system.py#L24-L32
• https://github.com/googleapis/python-scheduler/blob/9e139351d958149032f3efa9120d9e8b8232b4e8/tests/system.py#L20-L26
• https://github.com/googleapis/python-tasks/blob/674e8ee37f3cb94d1fe3b2c33f885a2f6612bf9e/tests/system/gapic/v2/test_system_tasks_v2.py#L20-L27
• https://github.com/googleapis/python-texttospeech/tree/b85a47c63e12810d7badbd3336a12db9eace917f/tests/system
• https://github.com/googleapis/python-videointelligence/blob/10422c3d5b9efb281ff11f45d84b5e9bfde8ab59/tests/system/test_system.py