The [auth] admin_project_name option was introduced in tempest 12.0.0
by [1]. Because the current lower bound of tempest is higher than it,
we can safely assume that the option always exists.
[1] ed6e586b9f8f0ada10af7711f297afa01b2b7754
Change-Id: I90dbeffd18fa073b34ded7ea6e2e2a3bad624cd6
fb142a09f8