Investigate usecases for local gRPC test harness

MR !135 (merged) converts the existing code of 'mock' coordinator and exporter which was using the crossbar implementation to use the new gRPC approach that is now being used by Labgrid.

After implementing this, there was some uncertainty about what the usecase is for this piece of functionality.

The original usecase was to allow us to test out the managers like the acquire and reserve managers using the distributed infrastructure approach, and being able to run that in CI without additional CI infrastructure and is faster than using full emulation like QEMU.

This issue involves using the functionality for that particular usecase along with exploring what other usecases this functionality would solve.