added LifeCycle methods and lazy executor service init to ContextBase

Since ContextBase has never before implemented LifeCycle, there are lots
of existing uses (in tests) that would need to be modified if calling
the LifeCycle methods is made a strict requirement.  By using a lazy
initialization of executor service, we can allow existing uses to ignore
the lifecycle methods, and focus our attention on those few cases where
it calling the stop method really matters.