ipa_sidgen: Allow sidgen_task to continue after finding issues
    
    find_sid_for_ldap_entry could fail in several ways if a Posix ID can not
    be converted to an unused SID. This could happen for example for ducplicate
    IDs or user/group out of range.
    
    This change enables ipa_sidgen_task to continue in the error case to try
    to convert the entries without errors. The error messages have been
    extended to additionally show the DN string for the bad entries.
    
    Fixes: https://pagure.io/freeipa/issue/9618
    
    Signed-off-by: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>