Expose workers within scheduler

[Balearica]

Overview

We should add an interface for directly accessing all workers in a scheduler.

Motivation

Say you have a scheduler that contains 4 workers, and want to change some configuration parameter on all workers. This is a reasonable thing to want, however there is currently no easy way to do this.

1. Passing a setParameters job through the scheduler is not correct, as the scheduler assumes all workers are homogenous and assigns jobs to the next available worker
2. Directly accessing the workers in a scheduler is not currently possible

Therefore, one would need to create a separate array and add all workers to that array in addition to adding them to the scheduler.