Also fixes an msys (git-bash) incompatibility, similar to the one
fixed in crrev.com/4845f0ed.

This change doesn't actually use the wrapper in any new places, but
subsequent changes will be made to use it in places where
'exec python' is called directly, like gclient and fetch.

BUG=411518
R=iannucci@google.com

Review URL: https://codereview.chromium.org/1415993003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297357 0039d316-1c4b-4281-b951-d872f2087c98