Keystone: manage multiple roles for admin@admin

To make Heat working properly with admin tenant, it needs to have
"heat_stack_owner" role.
So let's add a new parameter that fits with a patch upstream [1]
that will allow us more flexibility to manage roles for admin
tenant/user.

Also need to go up in the commits for puppet-keystone (manage role
support).
[1] https://review.openstack.org/#/c/132350/
Merge pull request #711 from enovance/fix-admin-tenant

Keystone: manage multiple roles for admin@admin