test-interest-aggregation: test case to test NFD's interest aggregation

Change-Id: I7b84e0d77d285b4ef85a3b1850a0cc953cfc05b3
refs: #1384
diff --git a/library_helpers/process_manager.py b/library_helpers/process_manager.py
index 204d61d..ac53b0f 100644
--- a/library_helpers/process_manager.py
+++ b/library_helpers/process_manager.py
@@ -70,7 +70,7 @@
         self.processes[processKey].start()
 
     def killProcess(self, processKey):
-        if processKey not in self.results:
+        if processKey not in self.results and processKey in self.subprocesses:
             self.subprocesses[processKey].terminate()
 
     def hasProcessCompleted(self, processKey):