Add call depth check to executor instrumentation

[laurit]

Lets assume we are trying to exclude a task from context propagation with IgnoredTypesBuilder.ignoreTaskClass. When code calls AbstractExecutorService.submit(Runnable) we'll correctly see that the actual task class is excluded and skip propagation. Now that method wraps the task into a FutureTask and calls execute(Runnable) which we also instrument. Since the task has been wrapped we'll allow context propagation. Call depth check should ensure that we skip instrumentation in nested calls.