shutdown search executor at the end of indexing

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/index/Indexer.java

@@ -413,6 +413,7 @@ public static void main(String[] argv) {
             System.err.println("Exception: " + e.getLocalizedMessage());
             System.exit(1);
         } finally {
+            env.getSearchExecutor().shutdownNow();
             stats.report(LOGGER, "Indexer finished", "indexer.total");
         }
     }