Fix owner_or_admin API tests

lb_observer and lb_global_observer don't have any meaning when
admin_or_owner policy override in enabled.
This commit disables client creation for those roles and removes their
uses from API tests (the behavior of the owner_or_admin tests are now
similar to their behavior before the introduction of the new RBAC
tests).

Requires the following configuration in tempest.conf:

[load_balancer]
RBAC_test_type = owner_or_admin
member_role = member
admin_role = admin

Change-Id: I2231384933d5974b962a558e8c0b3bffb1140b5a
9 files changed