fixes #2747

WriteBehindManager start() and stop() methods are enhanced.added test method.
Why don't your store the scheduledExecutor as a field? The executionService is only needed in the constructor when you obtain a reference to the scheduledExecutor. This way you class becomes simpler since the executionService become a small detail in the constructor instead of something visible throughout the class. Then you only store the scheduledExecutor and you don't need to palce executorName and executionService as fields in the object (the less fields... often.. the better).

So what is the reason you dropped the old approach?