Disable flaky qp_union_intersect test

This commit amends commit d63731d. Fallback needs to happen inside the
rollback'd transaction as that is where the stale cache entry is not
cleaned up properly.

Author: dgkimura

src/test/regress/expected/qp_union_intersect.out

@@ -1687,6 +1687,8 @@ rollback;
 -- @description union_update_test28: Negative Tests Update the partition key to an out of dml_union_range value with no default partition
 begin;
 DROP TABLE dml_union_s_1_prt_def;
+-- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
+set optimizer=off;
 SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
  count 
 -------
@@ -1699,9 +1701,8 @@ DETAIL:  Partition key of the failing row contains (d) = (null).
 --SELECT DISTINCT(d) FROM dml_union_s;
 --SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
 rollback;
+reset optimizer;
 -- @description union_update_test29: Negative Tests  UPDATE violates the CHECK constraint on the column
--- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
-set optimizer=off;
 SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
  count 
 -------
@@ -1711,7 +1712,6 @@ SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 UPDATE dml_union_s SET b = (SELECT NULL UNION SELECT NULL)::numeric;
 ERROR:  null value in column "b" of relation "dml_union_s_1_prt_2" violates not-null constraint  (seg0 127.0.1.1:7002 pid=773223)
 DETAIL:  Failing row contains (5, null, s, 5).
-reset optimizer;
 --SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 --SELECT DISTINCT(b) FROM dml_union_s;
 -- @description union_update_test30: Negative Tests  more than one row returned by a sub-query used as an expression

src/test/regress/expected/qp_union_intersect_optimizer.out

@@ -1688,6 +1688,8 @@ rollback;
 -- @description union_update_test28: Negative Tests Update the partition key to an out of dml_union_range value with no default partition
 begin;
 DROP TABLE dml_union_s_1_prt_def;
+-- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
+set optimizer=off;
 SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
  count 
 -------
@@ -1700,9 +1702,8 @@ DETAIL:  Partition key of the failing row contains (d) = (null).
 --SELECT DISTINCT(d) FROM dml_union_s;
 --SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
 rollback;
+reset optimizer;
 -- @description union_update_test29: Negative Tests  UPDATE violates the CHECK constraint on the column
--- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
-set optimizer=off;
 SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
  count 
 -------
@@ -1712,7 +1713,6 @@ SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 UPDATE dml_union_s SET b = (SELECT NULL UNION SELECT NULL)::numeric;
 ERROR:  null value in column "b" violates not-null constraint  (seg0 127.0.0.1:7002 pid=31287)
 DETAIL:  Failing row contains (1, null, s, 1).
-reset optimizer;
 --SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 --SELECT DISTINCT(b) FROM dml_union_s;
 -- @description union_update_test30: Negative Tests  more than one row returned by a sub-query used as an expression

src/test/regress/sql/qp_union_intersect.sql

@@ -619,18 +619,18 @@ rollback;
 -- @description union_update_test28: Negative Tests Update the partition key to an out of dml_union_range value with no default partition
 begin;
 DROP TABLE dml_union_s_1_prt_def;
+-- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
+set optimizer=off;
 SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
 UPDATE dml_union_s SET d = (SELECT NULL EXCEPT SELECT NULL)::numeric; 
 --SELECT DISTINCT(d) FROM dml_union_s;
 --SELECT COUNT(DISTINCT(d)) FROM dml_union_s;
 rollback;
+reset optimizer;
 
 -- @description union_update_test29: Negative Tests  UPDATE violates the CHECK constraint on the column
--- GPDB_12_MERGE_FIXME: This test case is flaky, ERROR:  expected partdefid 134733, but got 0 (partdesc.c:194)
-set optimizer=off;
 SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 UPDATE dml_union_s SET b = (SELECT NULL UNION SELECT NULL)::numeric;
-reset optimizer;
 --SELECT COUNT(DISTINCT(b)) FROM dml_union_s;
 --SELECT DISTINCT(b) FROM dml_union_s;