Fix AutoScalerPolicy

- We didn't have tearDown, so for "repeated" test with invocationCount=100
  we were presumably having 100 app+policies running, with lots
  of threads etc
- Also tidied up some of the assertion code to improve messages
Use Entities.destroyAll to tear down tests

- It terminates the management context, as well as stopping the app
Fix JavaEntityTest.testPolicySubscribesToEvents

- test was not creating a new entity, and relied on accidental test
  ordering for the entity field to have been set
Name our threads

- Pass in thread factory wherever we're creating an executor
- Adds TODO comments where we're creating an executor, and we should
  instead be (somehow) reusing the execution manager's pool
LoadBalancingPolicyTest: destroy policy

- so we kill the internal executor of the policy