tests: add get_or_create

[odeke-em]

Ran the various component tests in get_or_create,
filed and grouped tests that fail due to lack of savepoints
in Cloud Spanner, following Tim's advisory in #384.

Fixes #270
Fixes #384

[timgraham]

As said at #270 (comment), I believe the remaing skips should be grouped with 'test_utils.tests.TestBadSetUpTestData.test_failure_in_setUpTestData_should_rollback_transaction'" under the title "Tests that require savepoints."

[odeke-em]

As said at #270 (comment), I believe the remaing skips should be grouped with 'test_utils.tests.TestBadSetUpTestData.test_failure_in_setUpTestData_should_rollback_transaction'" under the title "Tests that require savepoints."

Thank you @timgraham! I've added those suggestions and updated this PR with the corresponding issues, and the features.py entries.

[timgraham]

Are all those tests actually failing? (The previous list was shorter, I thought?) I think CockroachDB is a bit different because it supports transactions but not savepoints while Spanner doesn't support transactions nor savepoints.

[odeke-em]

Are all those tests actually failing? (The previous list was shorter, I thought?) I think CockroachDB is a bit different because it supports transactions but not savepoints while Spanner doesn't support transactions nor savepoints.

I blindly copied all the mentioned tests in #270 (comment), without any thought. Sure let me re-audit by enabling and running the newly skipped tests, it should take about 12 minutes or so to finish running locally.

[odeke-em]

@timgraham results came back

test_get_or_create_invalid_params (get_or_create.tests.GetOrCreateTests) ... ok
test_create_with_duplicate_primary_key (get_or_create.tests.GetOrCreateTestsWithManualPKs) ... ok
test_get_or_create_raises_IntegrityError_plus_traceback (get_or_create.tests.GetOrCreateTestsWithManualPKs) ... ok
test_savepoint_rollback (get_or_create.tests.GetOrCreateTestsWithManualPKs) ... ok
test_something (get_or_create.tests.GetOrCreateThroughManyToMany) ... ok
test_integrity (get_or_create.tests.UpdateOrCreateTests) ... ERROR
test_manual_primary_key_test (get_or_create.tests.UpdateOrCreateTests) ... ERROR
test_create_with_duplicate_primary_key (get_or_create.tests.UpdateOrCreateTestsWithManualPKs) ... ERROR

There were only 3 failing tests so back to the short list, please take a look and thanks again!