Stop running shells when closing host handler.

cloudcontrol/node/host/__init__.py

@@ -178,6 +178,14 @@ class Handler(BasePlugin):
         # running shells
         self.shells = dict()
 
+    def stop(self):
+        # kill all currently running shells
+        for shell in self.shells.values():
+            shell.kill()
+            shell.close_cb()
+        self.shells.clear()
+        BasePlugin.stop(self)
+
     def execute_command(self, command):
         """Execute an arbitrary shell command on the host.