- n.node used the n.lock as underlaying locker. The service loop initially
locked it, the Notify function tried to lock it before calling n.node.Signal,
leading to a dead-lock.
- the go routine calling ChangeMaster was not synchronized with the Notify
method. The former was triggering change events that the later never saw
when the former's startup was faster that of Notify. Hence, not even a single
event was noticed and not even a single start/stop call of the slow service
was triggered.
This patch replaces the n.node condition object with a simple channel n.changed.
The service loop watches it.
Updating the notified private variables is still protected with n.lock against
races, but independently of the n.changed channel. Hence, the deadlock is gone.
Moreover, the startup of the Notify loop is synchronized with the go routine which
changes the master. Hence, the Notify loop will see the master changes.
Fixes#10776
