Fix uuid defaults
    
    Recently the uuid attributes for user and groups were removed because
    it was found that there are not used at all and that some of them where
    causing issues (https://fedorahosted.org/sssd/ticket/2383).
    
    The new views/overrides feature of FreeIPA uses the ipaUniqueID attribute
    to relate overrides with the original IPA objects. The previous two
    patches revert the removal of the uuid attributes from users and groups
    with this patch set the default value of these attributes to
    ipaUniqueID from the IPA provider, to objectGUID for the AD provider and
    leaves them unset for the general LDAP case to avoid issues like the one
    from ticket #2383.
    
    Related to https://fedorahosted.org/sssd/ticket/2481
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>