Neutron bobcat release has enabled the RBAC new defaults
by default. With the latest release of Neutron have new
defaults enable, we should configure the same by default in
devstack. This change make NEUTRON_ENFORCE_SCOPE flag to
True by default so that every job will run with Neutron
new defaults.
As old defaults are still supported (in deprecated way),
we will keep this flag so that we can have one job disable
it and test the old defaults.
Change-Id: I3361d33885b2e3af7cad0141f9b799b2723ee8a1