--allure-link-pattern option don't filter any test.

#### I'm submitting a ...
- [ X ] bug report
- [ ] feature request
- [ ] support request => Please do not submit support request here, see note at the top of this template.

#### What is the current behavior?

`--allure-link-pattern` option don't filter any test, and run the full suite.

#### If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

```python
import allure

@allure.testcase('https://redmine.xxx.com/issues/25','25')
def test_with_allure_link():
pass

def test_without_allure_link():
pass
```

```bash
(venv) bash-5.0$ python3 -m pytest --allure-link-pattern='testcase:https://redmine.xxx.com/issues/25'
======================================================================================= test session starts ========================================================================================
platform linux -- Python 3.7.4, pytest-5.0.1, py-1.8.0, pluggy-0.12.0
rootdir: /home/xxx/PycharmProjects/sandbox/bugs
plugins: allure-pytest-2.7.0
collected 2 items

test_allure_link.py .. [100%]

===================================================================================== 2 passed in 0.02 seconds =====================================================================================
```

#### What is the expected behavior?
`--allure-link-pattern` should only run the test with the matching link decorator.

#### Please tell us about your environment:

- Allure version: 2.8.1
- Test framework: pytest@5.1.2 also tested on 5.1.0
- Allure adaptor: allure-pytest@2.8.4 also tested on 2.7.0

#### Other information

```bash
python3 -m pytest --allure-link-pattern='testcase:https://redmine.xxx.com/issues/25'
============================= test session starts ==============================
platform linux -- Python 3.7.4, pytest-5.1.2, py-1.8.0, pluggy-0.12.0
rootdir: /server/xxx, inifile: pytest.ini, testpaths: features/tests
plugins: allure-pytest-2.8.4
collected 2772 items / 2 deselected / 2770 selected
```

Reproduce the behavior with the provided test_allure_link.py example and the pytest command using --allure-link-pattern. Start by tracing how allure-pytest registers the option and applies collection filtering; done means the linked test is selected while the unlinked test is deselected, with coverage for the reported case.

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