OAK-11027 flaky IncrementalStoreTest (#1979)

Author: thomasmueller

oak-run/src/test/java/org/apache/jackrabbit/oak/index/IncrementalStoreTest.java

@@ -709,6 +709,9 @@ private static List<String> getNodeStatesWithPrefferedPathsAndPathPredicatesOver
 
     private Backend createNodeStore(boolean readOnly) {
         MongoConnection c = connectionFactory.getConnection();
+        if (!readOnly) {
+            MongoUtils.dropCollections(c.getDatabase());
+        }
         DocumentMK.Builder builder = builderProvider.newBuilder();
         builder.setMongoDB(c.getMongoClient(), c.getDBName());
         if (readOnly) {