[clang-tidy] Python scripts shebang fixes

Summary:
This patch fixes shebang lines in Python script files.

Most Python scripts in LLVM & Clang are using this shebang line.

[[ https://mail.python.org/pipermail/tutor/2007-June/054816.html | Here]] is an explanaiton of why such line should be used instead of what is currently in these few files.

Reviewers: klimek, alexfh

Subscribers: cfe-commits

Patch by Kirill Bobyrev!

Differential Revision: http://reviews.llvm.org/D16270

llvm-svn: 258133