Reword error message for outer joins requiring repartition

We changed error message which appears when user tries to execute outer join command and
that command requires repartitioning. Old error message mentioned about 1-to-1 shard
partitioning which may not be clear to user.

src/backend/distributed/planner/multi_join_order.c

@@ -244,9 +244,10 @@ FixedJoinOrderList(FromExpr *fromExpr, List *tableEntryList)
 		{
 			/* re-partitioning for OUTER joins is not implemented */
 			ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							errmsg("cannot perform distributed planning on this query"),
-							errdetail("Shards of relations in outer join queries must "
-									  "have 1-to-1 shard partitioning")));
+							errmsg("cannot run outer join query if join is not on the "
+								   "partition column"),
+							errdetail("Outer joins requiring repartitioning are not "
+									  "supported.")));
 		}
 
 		if (joinType != JOIN_INNER)

src/test/regress/expected/multi_dropped_column_aliases.out

@@ -62,5 +62,5 @@ FROM   (customer LEFT OUTER JOIN orders ON (c_custkey = o_custkey)) AS
        test(c_custkey, c_nationkey)
        INNER JOIN lineitem ON (test.c_custkey = l_orderkey)
 LIMIT 10;
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.

src/test/regress/output/multi_outer_join.source

@@ -245,8 +245,8 @@ SELECT
 	count(*)
 FROM
 	multi_outer_join_left a LEFT JOIN multi_outer_join_right b ON (l_nationkey = r_nationkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- Anti-join should return customers for which there is no row in the right table
 SELECT
 	min(l_custkey), max(l_custkey)

src/test/regress/output/multi_outer_join_reference.source

@@ -214,8 +214,8 @@ SELECT
 	min(r_custkey), max(r_custkey)
 FROM
 	multi_outer_join_left_hash a RIGHT JOIN multi_outer_join_right_reference b ON (l_custkey = r_custkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- Reverse right join should be same as left join
 SELECT
 	min(l_custkey), max(l_custkey)
@@ -278,8 +278,8 @@ SELECT
 	count(*)
 FROM
 	multi_outer_join_left_hash a LEFT JOIN multi_outer_join_right_hash b ON (l_nationkey = r_nationkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- Anti-join should return customers for which there is no row in the right table
 SELECT
 	min(l_custkey), max(l_custkey)
@@ -337,8 +337,8 @@ SELECT
 	min(r_custkey), max(r_custkey)
 FROM
 	multi_outer_join_left_hash a RIGHT JOIN multi_outer_join_right_reference b ON (l_custkey = r_custkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- Reverse right join should be same as left join
 SELECT
 	min(l_custkey), max(l_custkey)
@@ -601,8 +601,8 @@ SELECT
 FROM
 	multi_outer_join_left_hash l1
 	FULL JOIN multi_outer_join_third_reference t1 ON (l1.l_custkey = t1.t_custkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- inner join  + single shard left join should work
 SELECT
 	l_custkey, r_custkey, t_custkey
@@ -676,8 +676,8 @@ FROM
 	multi_outer_join_third_reference t1
 	INNER JOIN multi_outer_join_left_hash l1 ON (l1.l_custkey = t1.t_custkey)
 	LEFT JOIN multi_outer_join_right_reference r1 ON (l1.l_custkey  = r1.r_custkey);
-ERROR:  cannot perform distributed planning on this query
-DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+ERROR:  cannot run outer join query if join is not on the partition column
+DETAIL:  Outer joins requiring repartitioning are not supported.
 -- inner (local) join  + 2 shards left (dual partition) join should work
 SELECT
 	l_custkey, t_custkey, r_custkey