Switch back to pep8+pyflakes, the current django-jenkins flake8 implementation seems not to work at all.
Switch back to pep8+pyflakes, the current django-jenkins flake8 implementation seems not to work at all.

```
Traceback (most recent call last):
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/django/core/management/base.py", line 222, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/django/core/management/base.py", line 255, in execute
    output = self.handle(*args, **options)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/management/commands/__init__.py", line 93, in handle
    if test_runner.run_tests(test_labels):
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/nose_runner.py", line 103, in run_tests
    result = BasicNoseRunner.run_tests(self, test_labels, extra_tests=None)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/django_nose/runner.py", line 155, in run_tests
    result = self.run_suite(nose_argv)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/nose_runner.py", line 92, in run_suite
    testRunner=text_test_runner)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/nose/core.py", line 118, in __init__
    **extra_args)
  File "/usr/lib/python2.7/unittest/main.py", line 95, in __init__
    self.runTests()
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/nose/core.py", line 197, in runTests
    result = self.testRunner.run(self.test)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/nose_runner.py", line 65, in run
    self.config.plugins.finalize(result)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/nose/plugins/manager.py", line 99, in __call__
    return self.call(*arg, **kw)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/nose/plugins/manager.py", line 167, in simple
    result = meth(*arg, **kw)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/django_nose/plugin.py", line 84, in finalize
    self.runner.teardown_test_environment()
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/runner.py", line 268, in teardown_test_environment
    signals.teardown_test_environment.send(sender=self)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/local/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 170, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/var/lib/jenkins/jobs/1flow/workspace/venv/src/django-jenkins/django_jenkins/tasks/run_flake8.py", line 61, in teardown_test_environment
    paths = flake8.run._get_python_files(locations)
AttributeError: 'module' object has no attribute '_get_python_files'
```

1flow/1flow,1flow/1flow,WillianPaiva/1flow,1flow/1flow,WillianPaiva/1flow,WillianPaiva/1flow,WillianPaiva/1flow,1flow/1flow,WillianPaiva/1flow,1flow/1flow