Fix TestImport for Windows by ensuring backslashes in the directory paths are...

Fix TestImport for Windows by ensuring backslashes in the directory paths are properly escaped in Python.

The Python import works by ensuring the directory of the module or package is in sys.path, and then it does a Python `import foo`.  The original code was not escaping the backslashes in the directory path, so this wasn't working.

Differential Revision: http://reviews.llvm.org/D18873

llvm-svn: 265738