Bug 216879

After r267368, run-webdriver-tests fails with the following trace:

Traceback (most recent call last):
  File "/app/webkit/Tools/Scripts/run-webdriver-tests", line 85, in <module>
    runner.run(args)
  File "/app/webkit/Tools/Scripts/webkitpy/webdriver_tests/webdriver_test_runner.py", line 70, in run
    runner_tests = [runner.collect_tests(tests) for runner in self._runners]
  File "/app/webkit/Tools/Scripts/webkitpy/webdriver_tests/webdriver_test_runner_selenium.py", line 51, in collect_tests
    executor = WebDriverSeleniumExecutor(self._driver, self._env)
  File "/app/webkit/Tools/Scripts/webkitpy/webdriver_tests/webdriver_selenium_executor.py", line 57, in __init__
    do_delayed_imports()
  File "/app/webkit/Tools/Scripts/webkitpy/webdriver_tests/webdriver_selenium_executor.py", line 35, in do_delayed_imports
    import webkitpy.webdriver_tests.pytest_runner as pytest_runner
  File "/app/webkit/Tools/Scripts/webkitpy/webdriver_tests/pytest_runner.py", line 32, in <module>
    import webkitpy.thirdparty.autoinstalled.pytest
  File "/app/webkit/Tools/Scripts/webkitpy/thirdparty/autoinstalled/pytest.py", line 9, in <module>
    from _pytest.config import main, UsageError, cmdline, hookspec, hookimpl
  File "/app/webkit/Tools/Scripts/webkitpy/thirdparty/autoinstalled/_pytest/config/__init__.py", line 10, in <module>
    import py
ImportError: No module named py

Likely because WebDriver's pytest relied on mozlog/mozprocess calls to `self._ensure_autoinstalled_dir_is_in_sys_path()` to inject the autoinstalled path.