PartitionManager: Shutdown background thread during deactivate

Fixes ONOS-1168.

Change-Id: I7fc4fa3787b552d958e148b96e6a6a9c51291ddb
diff --git a/core/store/dist/src/main/java/org/onosproject/store/intent/impl/PartitionManager.java b/core/store/dist/src/main/java/org/onosproject/store/intent/impl/PartitionManager.java
index c130432..b3e193e 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/intent/impl/PartitionManager.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/intent/impl/PartitionManager.java
@@ -86,6 +86,8 @@
 
     @Deactivate
     public void deactivate() {
+        executor.shutdownNow();
+
         leadershipService.removeListener(leaderListener);
         clusterService.removeListener(clusterListener);
     }