This fixes several cases where the partition table could become corrupt and
the whole cluster being stuck in VERIFYING state.

This also reduces the probability the have cells out of date when restarting
several storage nodes simultaneously.

At last, if a master node becomes primary again, a cluster must not be started
automatically if nodes with readable cells are missing, in order to avoid
a split of the database. This could happen if this master node was previously
forced to start it.