AD: talk to GC first even for local domain objects
    
    Related: https://fedorahosted.org/sssd/ticket/2070
    
    Since we are recommending to configure the POSIX attributes so that they
    are replicated to the Global Catalog, we can start connecting to the GC
    by default even for local users. If the object is not matches in the GC,
    there is a possibility to fall back to LDAP.