Make TaskScheduler.Builder be non-final

[EronWright]

For mocking purposes (w/ Mockito) it would be handy if the builder weren't final.

[spodila]

Our preference for Builder being final is to prevent incompatibilities across newer versions of Fenzo any Builders users create by extending it, Migrating such users to new versions of Fenzo will be painful if we allowed such extensibility. We also see similar pattern used in other places. For example, Protobuf generated Builders are final.
My understanding of this stackoverflow link is that you should be able to mock it.

[EronWright]

The link suggests using PowerMock, which adds complexity (for example, I was unable to use it in a certain scalatest scenario).

My scenario is that a certain class is provided an instance of TaskScheduler.Builder in its constructor. That class sets some of the callbacks (withLeaseRejectAction) on the builder, then builds and uses the scheduler. In the unit test for this class, I'd like to provide a mock builder, so that I can provide a mock scheduler to the class while also capturing the lease reject callback to test it. Despite your objections, a non-final builder would really help with this scenario. Go ahead and close if you still object, otherwise I'll send a patch.

[spodila]

Our preference hasn't changed, so closing this. Thank you for the input.