Skip enumeration requests in IPA and AD providers as well
    
    Checking the enum request in the underlying LDAP provider to skip it
    might be too late as the richer IPA or AD providers depend on having a
    useful result when the sdap request finishes.
    
    Move the enumeration check earlier instead and allow directly in the IPA
    or AD handler.
    
    Related:
    https://fedorahosted.org/sssd/ticket/2659
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    (cherry picked from commit 40bc389bc79bc41429b5a92d5ce75955f8eefaf5)