add a pytest.ini file (pytorch#53152)

Summary:
This shall fix the first three items of pytorch#52984 by adding a pytest.ini configuration file.

#### `--tb=short`
In a failure, pytest will not show the entire traceback nor the docstring.

- Without `--tb=short`:
<details>

```
$ pytest test/test_typing.py -k tensor_copy
================================================================== test session starts ===================================================================
platform linux -- Python 3.8.6, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /home/guilhermel/git/pytorch, configfile: pytest.ini
plugins: hypothesis-5.38.1, typeguard-2.10.0
collected 8 items / 7 deselected / 1 selected

test/test_typing.py F                                                                                                                              [100%]

======================================================================== FAILURES ========================================================================
______________________________________________________________ test_reveal[tensor_copy.py] _______________________________________________________________

path = '/home/guilhermel/git/pytorch/test/typing/reveal/tensor_copy.py', reveal = 'int '
expected_reveal = "/home/guilhermel/git/pytorch/test/typing/reveal/tensor_copy.py:11: note: Revealed type is 'torch.tensor.Tensor'", lineno = 11

    def _test_reveal(path: str, reveal: str, expected_reveal: str, lineno: int) -> None:
        if reveal not in expected_reveal:
>           raise AssertionError(_REVEAL_MSG.format(lineno, expected_reveal, reveal))
E           AssertionError: Reveal mismatch at line 11
E
E           Expected reveal: "/home/guilhermel/git/pytorch/test/typing/reveal/tensor_copy.py:11: note: Revealed type is 'torch.tensor.Tensor'"
E           Observed reveal: 'int '

test/test_typing.py:156: AssertionError
================================================================ short test summary info =================================================================
FAILED test/test_typing.py::test_reveal[tensor_copy.py] - AssertionError: Reveal mismatch at line 11
```

</details>

- With `--tb=short`:
<details>

```
$ pytest test/test_typing.py -k tensor_copy
================================================================== test session starts ===================================================================
platform linux -- Python 3.8.6, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /home/guilhermel/git/pytorch, configfile: pytest.ini
plugins: hypothesis-5.38.1, typeguard-2.10.0
collected 8 items / 7 deselected / 1 selected

test/test_typing.py F                                                                                                                              [100%]

======================================================================== FAILURES ========================================================================
______________________________________________________________ test_reveal[tensor_copy.py] _______________________________________________________________
test/test_typing.py:156: in _test_reveal
    raise AssertionError(_REVEAL_MSG.format(lineno, expected_reveal, reveal))
E   AssertionError: Reveal mismatch at line 11
E
E   Expected reveal: "/home/guilhermel/git/pytorch/test/typing/reveal/tensor_copy.py:11: note: Revealed type is 'torch.tensor.Tensor'"
E   Observed reveal: 'int '
```

</details>

Pull Request resolved: pytorch#53152

Reviewed By: agolynski

Differential Revision: D26846808

Pulled By: walterddr

fbshipit-source-id: d16c951b370b0643c8bbedca73d5184c6b65aba7

Author: guilhermeleobas

pytest.ini

@@ -0,0 +1,12 @@
+[pytest]
+addopts =
+    # show summary of all tests that did not pass
+    -ra
+    # Make tracebacks shorter
+    --tb=native
+    # capture only Python print and C++ py::print, but not C output (low-level Python errors)
+    --capture=sys
+    # enable all warnings
+    -Wd
+testpaths =
+    test