GPO: Skip GPOs without gPCFunctionalityVersion
    
    We falsely stopped GPO processing when Group Policy Container
    in AD did not contain gPCFunctionalityVersion. Such GPOs
    should be ignored by SSSD according to MS-GPOL:
    https://msdn.microsoft.com/en-us/library/cc232538.aspx
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/3269
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit 6a490b312075d2588ad87bbb8a63466f1ac6a106)
    (cherry picked from commit 94903da8a3723094948b4b99b30f6449fed809da)