Fix a bug inside DistributedLock.extendExpiration():
Return false (as per API) if we don't hold the lock.

Change-Id: Id3c314f6e374c92a73ce6f1aa4b6fbcef0a80697
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLock.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLock.java
index a3fbc0d..48a45c4 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLock.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLock.java
@@ -132,6 +132,7 @@
         if (!isLocked()) {
             log.warn("Ignoring request to extend expiration for lock {}."
                     + " ExtendExpiration must be called for locks that are already acquired.", path);
+            return false;
         }
 
         if (databaseService.putIfValueMatches(