stop poller threads on shutdown

make sure module methods are not called after shutdownModule

+ fix: when mod.enablePoll is False, pollInfo is None
  therefore we have to check before access

Change-Id: I83b28607b25996376939175be8abf0c5b27bcac1

frappy/secnode.py

@@ -19,6 +19,7 @@
 #
 # *****************************************************************************
 
+import time
 import traceback
 from collections import OrderedDict
 
@@ -255,6 +256,15 @@ class SecNode:
 
     def shutdown_modules(self):
         """Call 'shutdownModule' for all modules."""
+        # stop pollers
+        for name in self.modules:
+            self.modules[name].stopPollThread()
+            # do not yet join here, as we want to wait in parallel
+        now = time.time()
+        deadline = now + 5
+        for name in self.modules:
+            self.modules[name].joinPollThread(now - deadline)
+            now = time.time()
         for name in self._getSortedModules():
             self.modules[name].shutdownModule()