UTIL: Convert domain->disabled into tri-state with domain states
    
    Required for:
    https://fedorahosted.org/sssd/ticket/2637
    
    This is a first step towards making it possible for domain to be around,
    but not contacted by Data Provider.
    
    Also explicitly create domains as active, previously we only relied on
    talloc_zero marking dom->disabled as false.
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>