Revert "qemu: emit error when trying to update blkiotune group_name in qemuDomainChangeDiskLive"
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1601677
    
    This reverts commit 047cfb05ee949325e77726531fd381820be8dc62
    Using numeric comparison on strings means we reject every update
    that does include the group name, even if it's unchanged.
    
    Signed-off-by: Ján Tomko <jtomko@redhat.com>
    Reviewed-by: Laine Stump <laine@laine.org>