Use scope in v3 identity client

Certain identity v3 API calls require a domain scoped token when
policy.v3cloudsample.json is used.
Introduce a new config flag to tell Tempest that keystone in the
targe cloud requires domain scoped tokens for admin actions.
Modify the v3 client managers used to obtain v3 admin identity
clients to request the domain scope when the flag is turned on.

Co-authored by: Roxana Gherle <roxana.gherle@hp.com>
Change-Id: I91ca907992428a5a14fb8d48a4fad105d2906e27
7 files changed