Remove admin role name 'admin' hardcode

[OpenStack Infra]

https://review.openstack.org/323953
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
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commit 0a8b2062dbde7f1a69a5f6cff52fb4f6a6effe61
Author: Paul Karikh <email address hidden>
Date: Tue Sep 30 14:53:21 2014 +0400

    Remove admin role name 'admin' hardcode

    Because of hardcoding name as the 'admin' was impossible to
    use administrative panel with a custom administrative role name.
    This fix replaces hardcoding the name of the administrative role
    with RBAC policy check.

    DocImpact
    Related commit: https://review.openstack.org/#/c/123745/
    Change-Id: I05c8fc750c56f6f6bb49a435662e821eb0d6ba30
    Closes-Bug: #1161144
    (cherry picked from commit ce5fb26bf5f431f0cdaa6860a732338db868a8fb)

[Rob Cresswell (robcresswell-deactivatedaccount)]

Fixed by https://review.openstack.org/#/c/364810/