StormExecutor: adding an unit test to changes introduced in STORM-3693

[reiabreu]

What is the purpose of the change

StormExecutor: adding an unit test to check if the RotatingMap' rotate is called only once when timing out tuples.

StormExecutor requires a considerable effort to mock and the pending map (which is RotatingMap) is an internal attribute. JUnit's reflection was used to mock the RotationMap and verify how many times rotate was called.

This test is far from optimal and I'm not a fan of using reflection, but will make it easier to detect regressions.
The test should be refactored in the future.

Additionally, refactored the changes introduced in #3828: boolean isSpout = this instanceof SpoutExecutor; should not be in Executor. A parent class should not have references to subclasses

How was the change tested

mvn clean install. All tests are passing.

[rzo1]

This test is far from optimal and I'm not a fan of using reflection, but will make it easier to detect regressions.
The test should be refactored in the future.

Maybe add an issue for it, so we can keep tracking it. Note: INFRA will soon migrate to GitHub Issues :)