corosync: Add cfg_trackstart/stop calls

corosync shutdown tracking has been broken for ages (since the
trackstart/stop calls were removed in 2012), so pacemaker has not been
able to veto corosync shutdown requests.

The corosync_cfg_startstart/stop calls have now been re-added back to
corosync and with this patch, the pacemaker shutdown veto will
work again (provided shutdown is done as a REQUEST rather then
REGARDLESS or IMMEDIATE of course). There is a new flag (--force
added to corosync-cfgtool -H which uses REGARDLESS.