title: ScopeMismatch on using session scoped fixture with pytest-mozwebqa plugin for py.test
body: <p>I am using <code>pytest-mozwebqa</code> plugin for running some selenium tests. I want to login to the application only once for all the tests so I tried using a session scoped fixture in the <code>conftest.py</code> but I am getting following error. How can I write this login fixture so that login is not required per test and a single login is available to all tests?</p>
  
  <p>This is the error I am getting:</p>
  
  <pre><code>================================================================================================= ERRORS ==================================================================================================
  ___________________________________________________________________________ ERROR at setup of TestData.test_selected_version ____________________________________________________________________________
  ScopeMismatch: You tried to access the 'function' scoped fixture 'mozwebqa' with a 'module' scoped request object, involved factories
  conftest.py:6:  def login(mozwebqa, variables)
  ../../.virtualenvs/webqa/lib/python2.7/site-packages/pytest_mozwebqa/pytest_mozwebqa.py:159:  def pytest_funcarg__mozwebqa(request)
  </code></pre>
  
  <p>Content of the <code>conftest.py</code>:</p>
  
  <pre><code>@pytest.fixture(scope='session')
  def login(mozwebqa, variables):
      data_page = DataPage(mozwebqa)
      network_page = data_page.select_version(variables)
      return network_page
  </code></pre>