bugfix getAndClearSlowQueries test

Author: rashtao

src/test/java/com/arangodb/ArangoDatabaseTest.java

@@ -928,6 +928,8 @@ public void run() {
 
     @Test
     public void getAndClearSlowQueries() {
+        db.clearSlowQueries();
+
         final QueryTrackingPropertiesEntity properties = db.getQueryTrackingProperties();
         final Long slowQueryThreshold = properties.getSlowQueryThreshold();
         properties.setSlowQueryThreshold(1L);