Python: stub out windows libraries for testing on linux

Here's a quick way to stub out windows libraries when you are testing on Linux. This code creates empty modules using imp.

  import imp
  import sys

  def testMethodWithWindowsCall():
    StubOutWindowsLibs()
    import windows_utils
  
  def StubOutWindowsLibs():
    pywintypes = imp.new_module("pywintypes")
    pywintypes.error = Exception
    sys.modules["pywintypes"] = pywintypes