Change CLI tests to use auth providers

This commit changes the CLI tests to use the auth providers for
credentials. Previously they were just using the admin credentials
straight from the config file. The typical motivation for doing this
would be tenant isolation for running in parallel, but that doesn't
apply to the CLI tests because they are simple read-only. However, in
the future when test-accounts supports admin credentials doing this
won't be supported.

Change-Id: Iad5fe6e8abe4491d10e9a676a1c2a7da05a38113
Merge "Change CLI tests to use auth providers"
Merge branch 'master' of https://github.com/openstack/tempest