SLIDER-94 move from fixed event callback to Callable  & futures; more generic and java-8 ready. This commit adds the new callback classes, but doesn't switch the AM to it
SLIDER-112 core test standalone agent AM tests failing
SLIDER-94 cleanup of TestWorkflowCompositeService
SLIDER-111 SLIDER-112 Merge branches
Conflicts:
	slider-core/src/test/groovy/org/apache/slider/agent/actions/TestActionExists.groovy
	slider-core/src/test/groovy/org/apache/slider/agent/actions/TestActionList.groovy
Merge branch 'feature/SLIDER-94_Get_YARN_utility_features_into_yarn-common' into develop