Use service user for nova service-to-service API tests

Nova has service-to-service internal APIs which are now
default to service role[1]. Token passed to
Nova needs to have 'service' role so that Nova use
service token auth data to validate if request is from
the OpenStack services or not.

Tempest test for server external event and volume swap
needs to add 'admin' role also in service user because
Nova need to access the server or volume resource of other
project which need 'admin' role.

Depends-On: https://review.opendev.org/c/openstack/devstack/+/958612

[1] https://review.opendev.org/c/openstack/nova/+/957578

Change-Id: I56ed7663ae1ffe4377a644d307e02921c3982fa5
Signed-off-by: Ghanshyam Maan <gmaan@ghanshyammann.com>
4 files changed