Crash when keys are rotated
This crash happens when leaving a test phone to do nothing (see https://code.briarproject.org/akwizgran/briar/merge_requests/74#note_2358):
java.lang.IllegalStateException: TimerTask is scheduled already
at java.util.Timer.scheduleImpl(Timer.java:569)
at java.util.Timer.schedule(Timer.java:456)
at org.briarproject.system.SystemTimer.schedule(SystemTimer.java:21)
at org.briarproject.transport.TransportKeyManager.run(TransportKeyManager.java:260)
at java.util.Timer$TimerImpl.run(Timer.java:284)
Looks like the issue is that TransportKeyManager re-schedules the same TimerTask instance (i.e. itself) and the Timer impl doesn't allow that. TransportKeyManager's TimerTask implementation should be broken out into a private class so a different instance can be scheduled each time.