Switching rbac role can be achieved by admin credential manager rather explicitly passing admin client from caller

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Current Framework Implementation:

During RBAC testing,

In rbac_utils.py file, for switching role we are using "admin_client" (which is coming as part of "caller") for role deletion and role assignment.

For this purpose, in rbac_base.py file (or in testcase file)we need to define "admin_client".
Again for admin_client we need "admin" credentials defined in rbac_base also.

i.e. credentials = ['primary', 'admin']

In the rbac base we are writing"credentials = ['primary', 'admin']", which in turn will create 2 tenants -
1. "primary" tenant (Which is inturn "admin" because in tmpest.conf we are passing tempest_roles="admin" which will be added to primary also)
2. "admin" tenant

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Problem with above Implementation :

1. In rbac_utils.py file, to delete all roles and assign role we again need to pass admin_client though caller which is also not a good idea. Because it mandates declaration of "admin" credentials in rbac_base.

2. During RBAC testing In tempest.conf "tempest_roles" is always hard coded to "admin", this becomes a precondition.

3. As "tempest_roles = admin", created "primary" tenant also becomes admin. In "credentials = ['primary', 'admin']" after primary which become admin because of tempest_roles=admin, we are again using "admin" tenant.
When both ('primary' and 'admin') has admin roles then using both of them is not an wise idea.

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Solution:
1. For above problem 1 -
        instead of passing "admin_client" in caller to rbac_utils, how about using admin credential manager from tempest ?

2. For above problem#2 and problem#3
       After implementation of solution#1, we need not to hard code tempest_roles to admin by using following things -

            a. Implement solution#1
            b. In rbac_base file (or in test case file ) use only admin credentials and drop primary credentials completely
             i.e. credentials = ['admin'] . Although we can use alt credentials
             c. As during test case writing we are using cls.os and cls.os_adm where (In tempest) cls.os comes from "primary" and cls.os_adm comes from "admin" credentials.
                  In our tests, we are using cls.os and cls.os_adm a number of times for client creation and other many more thing.
                  When we are dropping "primary" completely, cls.os will be gone.
                  Also in existing framework, cls.os and cls.os_adm, both are admin because of tempest_roles=admin.
                  With the idea why not we should keep single admin, after dropping "primary" we have to assign "cls.os = cls.os_adm" in setup_credentials
                 So, In rbac_base file, we have to write following lines -

               @classmethod
              def setup_credentials(cls):
                  super(<BaseClass>, cls).setup_credentials()
                  cls.os = cls.os_adm

#Solution Proposed
Following patches tries to fulfill above things -
    https://review.openstack.org/#/c/433741/