Fixing jenkins failures

I prefer `succeedsEventually`. It is more consistent with how our other tests are written, and more concise. The other parameters to the repeater are just noise. This test should not care what the repeat interval or duration is.

    Asserts.succeedsEventually(new Runnable() {
        public void run() {
            forceGc();
            ExecutionManager execManager = ((EntityInternal)entity).getManagementContext().getExecutionManager();
            Collection<Task<?>> tasks = BrooklynTaskTags.getTasksInEntityContext(execManager, entity);
            assertEquals(tasks.size(), expectedCount, "Tasks were "+tasks);
        }});