Adds metadata-flavor header that gcloud-auth-library checks for
Adds metadata-flavor header that gcloud-auth-library checks for

parthea/datalab,googledatalab/datalab,yebrahim/datalab,googledatalab/datalab,parthea/datalab,craigcitro/datalab,googledatalab/datalab,parthea/datalab,craigcitro/datalab,yebrahim/datalab,parthea/datalab,googledatalab/datalab,parthea/datalab,parthea/datalab,googledatalab/datalab,googledatalab/datalab,yebrahim/datalab,yebrahim/datalab,yebrahim/datalab,craigcitro/datalab,craigcitro/datalab,craigcitro/datalab