text: Title: Allure throws UnicodeDecodeError when recieve \\u in test parameter value
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  #### 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 cant escape test name when meet `\\u` in test parameter value and throws UnicodeDecodeError exception.
  
  #### Reproduction
  Run code below with argument `--alluredir=somedir` 
  ```python
  import pytest
  @pytest.mark.parametrize('param', ['\\u'])
  def test_decode_error( param):
      pass
  ```
  Trace:
  ```
  pytest test_allure.py --alluredir=allure-results -v
  ============================= test session starts =============================
  platform win32 -- Python 2.7.15, pytest-3.7.1, py-1.5.4, pluggy-0.7.1 -- c:\git\allure_error\venv\scripts\python.exe
  cachedir: .pytest_cache
  rootdir: C:\GIT\allure_error, inifile:
  plugins: allure-pytest-2.5.0
  collected 1 item
  
  test_allure.py::test_decode_error[C:\source\unigine.vcxproj-/p:Platform=x64] ERROR [100%]
  
  =================================== ERRORS ====================================
   ERROR at setup of test_decode_error[C:\source\unigine.vcxproj-/p:Platform=x64]
  
  self = <allure_pytest.listener.AllureListener object at 0x06697590>
  item = <Function 'test_decode_error[C:\\source\\unigine.vcxproj-/p:Platform=x64]'>
  
      @pytest.hookimpl(hookwrapper=True)
      def pytest_runtest_setup(self, item):
          uuid = self._cache.set(item.nodeid)
          test_result = TestResult(name=item.name, uuid=uuid)
          self.allure_logger.schedule_test(uuid, test_result)
  
          yield
          uuid = self._cache.get(item.nodeid)
          test_result = self.allure_logger.get_test(uuid)
          for fixturedef in _test_fixtures(item):
              group_uuid = self._cache.get(fixturedef)
              if not group_uuid:
                  group_uuid = self._cache.set(fixturedef)
                  group = TestResultContainer(uuid=group_uuid)
                  self.allure_logger.start_group(group_uuid, group)
              self.allure_logger.update_group(group_uuid, children=uuid)
          params = item.callspec.params if hasattr(item, 'callspec') else {}
  
  >       test_result.name = allure_name(item, params)
  
  venv\lib\site-packages\allure_pytest\listener.py:78:
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  venv\lib\site-packages\allure_pytest\utils.py:88: in allure_name
      name = escape_name(item.name)
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  
  name = 'test_decode_error[C:\\source\\unigine.vcxproj-/p:Platform=x64]'
  
      def escape_name(name):
          if six.PY2:
              try:
                  name.decode('string_escape').encode('unicode_escape')
              except UnicodeDecodeError:
                  return name.decode('string_escape').decode('utf-8')
  >       return name.encode('ascii', 'backslashreplace').decode('unicode_escape')
  E       UnicodeDecodeError: 'unicodeescape' codec can't decode bytes in position 27-28: truncated \uXXXX escape
  
  venv\lib\site-packages\allure_pytest\utils.py:108: UnicodeDecodeError
  ```
  
  #### Environment:
  
  - Allure version:        2.7.0
  - Test framework:        pytest@3.7.1
  - Allure adaptor:        allure-pytest@2.5.0
  - Python version:    2.7.15
  
  #### Other information 
  Without `--alluredir` argument exception is not appears
  
  [//]: # (
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