Configuring the Synchronizer's view duration

[meling]

We currently do something like this (in other code):

	var sync modules.Synchronizer
	if opts.GetLeaderRotation() == "fixed" {
		// fixed leader rotation uses the fixed view duration synchronizer
		sync = synchronizer.New(synchronizer.NewFixedViewDuration(opts.GetInitialTimeout().AsDuration()))
	} else {
		sync = synchronizer.New(synchronizer.NewViewDuration(
			uint64(opts.GetTimeoutSamples()),
			float64(opts.GetInitialTimeout().AsDuration().Nanoseconds())/float64(time.Millisecond),
			float64(opts.GetMaxTimeout().AsDuration().Nanoseconds())/float64(time.Millisecond),
			float64(opts.GetTimeoutMultiplier()),
		))
	}

Perhaps a better design would be to augment the LeaderRotation interface with a method that returns a ViewDuration that fits the specific leader rotation approach. But I'm not sure if it is easy to configure the leader rotation approach with the appropriate timeout values. Opening this issue to discuss and think more about this.

Alternatively, the LeaderRotation interface could return a Synchronizer directly.