Install python2 on existing checkouts

b/168835737

Change-Id: Ib482943f76243bbcd19b003f2063861db5c9faad
diff --git a/bootstrap/win/win_tools.bat b/bootstrap/win/win_tools.bat
index c6718ca..f24bda5 100644
--- a/bootstrap/win/win_tools.bat
+++ b/bootstrap/win/win_tools.bat
@@ -28,6 +28,7 @@
 :PYTHON_CHECK

 if not exist "%WIN_TOOLS_ROOT_DIR%\python276_bin" goto :PY27_INSTALL

 if not exist "%WIN_TOOLS_ROOT_DIR%\python.bat" goto :PY27_INSTALL

+if not exist "%WIN_TOOLS_ROOT_DIR%\python2.bat" goto :PY27_INSTALL

 set ERRORLEVEL=0

 goto :GIT_CHECK