Centralize and configure nova with cinder service user access
Centralize and configure nova with cinder service user access

Since Queens [1] nova has been able to be configured with
cinder service user credentials for operating on cinder
resources without a user auth token similar to things nova
needs to do without a user auth token for working with neutron
and placement resources.

This change:

- centralizes the nova [cinder] section configuration
- adds the necessary auth configuration

Needed by: https://review.opendev.org/549130/

[1] I3c35bba43fee81baebe8261f546c1424ce3a3383

Change-Id: I5640ee431f6856853f6b00ec7ed1ea21d05117dd

nawawi/openstack,nawawi/openstack,openstack-dev/devstack,openstack-dev/devstack