restructure google auth stuff into cpl, add utility script

git-svn-id: https://svn.osgeo.org/gdal/trunk@25478 f0d54148-0727-0410-94bb-9a71ac55c965
restructure google auth stuff into cpl, add utility script

git-svn-id: https://svn.osgeo.org/gdal/trunk@25479 f0d54148-0727-0410-94bb-9a71ac55c965