Really make 'gflags' optional.
Really make 'gflags' optional.

If it can't be imported, then we don't need to fix it up inside
'CredentialsFromFile'.

kevinli7/apitools,houglum/apitools,pcostell/apitools,cherba/apitools,b-daniels/apitools,betamos/apitools,google/apitools,craigcitro/original-apitools,craigcitro/apitools,thobrla/apitools