lxc: Sync BlkioDevice values when setting them in cgroups
    
    The problem here is that there are some values that kernel accepts, but
    does not set them, for example 18446744073709551615 which acts the same
    way as zero.  Let's do the same thing we do with other tuning options
    and re-read them right after they are set in order to keep our internal
    structures up-to-date.
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>