SERVER-9516 Give userAdminAnyDatabase more privs for v2.4 users; in support of upgrade.
SERVER-9516 Enhance privileges of builtin roles to handle auth upgrade system collections.

This commit lets userAdminAnyDatabase role run listDatabases, since it was the
only AnyDatabase role that couldn't.

It also uses constants for auth collections in RoleGraph.

Finally, it grants access to new_users and backup_users.