Build universal wheels

Since git-review is tested and works with both Python 2.x and 3.x
interpreters, we want to build py2.py3-none-any wheels rather than
just py2-none-any. Without this change the wheels created are only
retrieved by pip running under a Python 2.x interpreter, while
Python 3.x environments retrieve the tarball instead.

Change-Id: I4d0cd28095b9c0273c11f2a1a4b152ba3b2dca33
Merge "Build universal wheels"