ASTERIXDB-1005, ASTERIXDB-1263: Clean up subplan flattening:
1. Inline NestedTupleSource and remove SubplanOperator for special cases that
   join operators inside the SubplanOperator can be re-targeted for
   correlations;
2. Blindly inline NestedTupleSource and remove SubplanOperator for general cases
   where the condition of the special case is not met.

Change-Id: I4dd130a25f3c81272cc23f844ea20e376e990612
Reviewed-on: https://asterix-gerrit.ics.uci.edu/579
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Till Westmann <tillw@apache.org>
diff --git a/asterix-app/src/test/resources/optimizerts/results/nested_loj4.plan b/asterix-app/src/test/resources/optimizerts/results/nested_loj4.plan
new file mode 100644
index 0000000..340b115
--- /dev/null
+++ b/asterix-app/src/test/resources/optimizerts/results/nested_loj4.plan
@@ -0,0 +1,39 @@
+-- DISTRIBUTE_RESULT  |PARTITIONED|
+  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+    -- STREAM_PROJECT  |PARTITIONED|
+      -- ASSIGN  |PARTITIONED|
+        -- STREAM_PROJECT  |PARTITIONED|
+          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+            -- PRE_CLUSTERED_GROUP_BY[$$14]  |PARTITIONED|
+                    {
+                      -- AGGREGATE  |LOCAL|
+                        -- STREAM_SELECT  |LOCAL|
+                          -- NESTED_TUPLE_SOURCE  |LOCAL|
+                    }
+              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                -- STREAM_PROJECT  |PARTITIONED|
+                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                    -- HYBRID_HASH_JOIN [$$14][$$22]  |PARTITIONED|
+                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                        -- DATASOURCE_SCAN  |PARTITIONED|
+                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                            -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                        -- ASSIGN  |PARTITIONED|
+                          -- STREAM_PROJECT  |PARTITIONED|
+                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                              -- HYBRID_HASH_JOIN [$$22][$$16]  |PARTITIONED|
+                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                  -- STREAM_PROJECT  |PARTITIONED|
+                                    -- STREAM_SELECT  |PARTITIONED|
+                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                        -- DATASOURCE_SCAN  |PARTITIONED|
+                                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                            -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                -- HASH_PARTITION_EXCHANGE [$$16]  |PARTITIONED|
+                                  -- ASSIGN  |PARTITIONED|
+                                    -- STREAM_PROJECT  |PARTITIONED|
+                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                        -- DATASOURCE_SCAN  |PARTITIONED|
+                                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                            -- EMPTY_TUPLE_SOURCE  |PARTITIONED|