YARN-679 inner Launching logic with assertions and checks that Throwables get picked up and wrapped
YARN-679 executed services close unless execute=false on launch, at which point they don't even get executed
YARN-679 rm unused override
YARN-679 give all tests a TestService to identify their role and aid bulk mvn test runs
YARN-679 rename LaunchedService interface LaunchableService
YARN-679 test (and fix) that if a launched service -> stopped in startup, then it isn't execute()'d.
YARN-679 interrupt escalation rework (weak refs), tests of shutdown hook actions; lots of docs