Improving pipeline tests (#12784)

* Proposal

* Testing pipelines slightly better.

- Overall same design
- Metaclass to get proper different tests instead of subTest (not well
supported by Pytest)
- Added ANY meta object to make output checking more readable.
- Skipping architectures either without tiny_config or without
architecture.

* Small fix.

* Fixing the tests in case of None value.

* Oups.

* Rebased with more architectures.

* Fixing reformer tests (no override anymore).

* Adding more options for model tester config.

Co-authored-by: Lysandre <lysandre.debut@reseau.eseo.fr>

tests/test_modeling_mbart.py

@@ -90,7 +90,7 @@ class MBartModelTester:
         hidden_act="gelu",
         hidden_dropout_prob=0.1,
         attention_probs_dropout_prob=0.1,
-        max_position_embeddings=20,
+        max_position_embeddings=100,
         eos_token_id=2,
         pad_token_id=1,
         bos_token_id=0,