title: pytest command line argument failing
body: <p>I have added conftest.py at the same directory level as my test file . The content of my conftest.py : </p>
  
  <pre><code> import pytest
  
      def pytest_addoption(parser):
          parser.addoption("--l", action="store", help="Get license value")
      @pytest.fixture
      def lic(request):
          return request.config.getoption("--l")
  </code></pre>
  
  <p>and following is my test file def </p>
  
  <pre><code>   def  test(lic):
          print "testing license : %s"%lic
          assert 0
  </code></pre>
  
  <p>But i still get following error:</p>
  
  <pre><code>   pytest  .\source\test_latestLinuxAgent.py --l=test
          pytest : usage: pytest [options] [file_or_dir] [file_or_dir] [...]
          At line:1 char:1
          + pytest  .\source\test_latestLinuxAgent.py --l=test
  
  
          pytest: error: ambiguous option: --l=test could match --lf, --last-failed
  </code></pre>