bdr: Consider a sequence vote successfull in more scenarios.

bdr: Consider a sequence vote successfull in more scenarios.

If either there's no nays or the number of yays is bigger than the
concensus the vote can be considered successful. We don't want to
always wait for a majority of yays, because that'd possibly delay
voting for a long time, even if enough nodes for a consensus on
another chunk are online.