dissect: use DISKSEQ when waiting for block devices

dissect: use DISKSEQ when waiting for block devices

DISKSEQ is a reliable way to find out if we missed a uevent or not, as
it's monotonically increasing. If we parse an event with a smaller or
no sequence number, we know we need to wait longer. If we parse an
event with a greater sequence number, we know we missed it and the
device was reused.