Default working_dir for overcloud credential command
Default working_dir for overcloud credential command

parsed_args.working_dir was not defaulted to a value when it was not
specified, leading to a traceback.

Change-Id: I40073c57a7ca283ae913bd78c248bc4cf56da3a8
Signed-off-by: James Slagle <33ab48cedd1a7cf7a68e1b587db88f55f753652f@redhat.com>

openstack/python-tripleoclient