Keystone has supported system-scope since Queens and we already make
sure we create a cloud profile for system-admin in
/etc/openstack/clouds.yaml.
This commit ensures keystone creates a couple of new users to model
system-member and system-reader personas. Doing this by default in
devstack makes it easier for people to use.
We've already taken a similar approach in tempest by setting up the
various system personas for tempest clients to use.
Change-Id: Iceb7c5f517db20072e121dc7538abaa888423c67
021ae0bcc8