Fix test clang-diff-json.cpp

Summary:
This test would fail if the python path had spaces. Add a quote around the path to fix this problem and update some test values changed by the addition of quotes around the path.

Tested on Windows and Linux with Python 3.x

Reviewers: zturner, llvm-commits

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D43164

llvm-svn: 324824