Test Case: Integration test for starting a controller with pre-exiting instances.

[Cooldude2606]

During the development of #510 all tests were passing but when the controller was started from command line it would output a fatel error. The following test case will prevent regression in this area:

1. Mock / Create instances.json
2. Start a new instance of Controller
3. Assert everything started without errors

This is potentially a family of related tests covering: hosts.json, instances.json, mod-packs.json, users.json