Fix LoadTest (missing .startManagement call)
SimulatedXyzImpl: add SIMULATE_ENTITY config

- For SimulatedJBoss7ServerImpl etc, add a SIMULATE_ENTITY config
  option.
- If set, then don’t start the real entity (instead just run `sleep`
  or skip the step entirely)
- Should we useful for setting to false, while also setting
  simulateExternalMonitoring (in situations where there is enough
  underlying resource to run many app-servers!)
YAML support for specifying entity impl

- support was already there with `type: <concrete-class>`
- just added test
Support for supplying machine_details as config
This closes #224