Some tempest tests require that a specific role is available for use.
Add a new variable, `tempest_roles`, to allow users to provide a list of
roles to create.
The existing tasks that create the 'reseller_admin' and 'remote_image'
roles have been removed. The correctly named 'ResellerAdmin' role is
already created by the os_swift role and the 'remote_image' is no longer
required since the glance tests make use of an admin user.
Depends-On: I66b7c639494d98fdb3baa52fe56c670e32dea3ce
Change-Id: I7987c5a4dbf50e97322a5b348c3cbd817b2672d6
960422c5b9