Update stack.sh to use openstackclient commands

There were a few instances of keystoneclient still being used,
these were replaced with their openstackclient equivalent.

Change-Id: I47fb7cf949b9ab054b97ae387ecbc6d7070fa9c3
Merge "Update stack.sh to use openstackclient commands"
Merge branch 'master' of https://github.com/openstack-dev/devstack