google: Update generic auth error message
google: Update generic auth error message

Google authentication will fail if your time drift (difference between your local time and time on google servers) is bigger than 5 minutes. This often happens on the VM instances running in various cloud providers. Google itself doesn't provide any helpful indication of the issue, the response is just {u'error': u'invalid_grant'}.

mtekel/libcloud,mtekel/libcloud,mtekel/libcloud