Start remote transactions in master_append_table_to_shard

Add a call to RemoteTransactionBeginIfNecessary so that BEGIN is
actually sent to the remote connections. This means that ROLLBACK and
Ctrl-C are respected and don't leave the table in a partial state.

src/backend/distributed/master/master_stage_protocol.c

@@ -278,6 +278,8 @@ master_append_table_to_shard(PG_FUNCTION_ARGS)
 						 quote_literal_cstr(sourceTableName),
 						 quote_literal_cstr(sourceNodeName), sourceNodePort);
 
+		RemoteTransactionBeginIfNecessary(connection);
+
 		executeResult = ExecuteOptionalRemoteCommand(connection, workerAppendQuery->data,
 													 &queryResult);
 		PQclear(queryResult);

src/test/regress/input/multi_append_table_to_shard.source

@@ -138,5 +138,16 @@ WHERE	'multi_append_table_to_shard_date'::regclass::oid = logicalrelid;
 
 SELECT * FROM multi_append_table_to_shard_date;
 
+-- When run inside aborted transaction does not persist changes
+INSERT INTO multi_append_table_to_shard_stage VALUES ('2016-02-02', 4);
+BEGIN;
+SELECT	master_append_table_to_shard(shardid, 'multi_append_table_to_shard_stage', 'localhost', 57636)
+FROM
+		pg_dist_shard
+WHERE	'multi_append_table_to_shard_date'::regclass::oid = logicalrelid;
+ROLLBACK;
+
+SELECT * FROM multi_append_table_to_shard_date;
+
 DROP TABLE multi_append_table_to_shard_stage;
 DROP TABLE multi_append_table_to_shard_date;

src/test/regress/output/multi_append_table_to_shard.source

@@ -227,5 +227,26 @@ SELECT * FROM multi_append_table_to_shard_date;
  01-01-2016 |     3
 (3 rows)
 
+-- When run inside aborted transaction does not persist changes
+INSERT INTO multi_append_table_to_shard_stage VALUES ('2016-02-02', 4);
+BEGIN;
+SELECT	master_append_table_to_shard(shardid, 'multi_append_table_to_shard_stage', 'localhost', 57636)
+FROM
+		pg_dist_shard
+WHERE	'multi_append_table_to_shard_date'::regclass::oid = logicalrelid;
+ master_append_table_to_shard 
+------------------------------
+                    0.0266667
+(1 row)
+
+ROLLBACK;
+SELECT * FROM multi_append_table_to_shard_date;
+ event_date | value 
+------------+-------
+            |      
+            |      
+ 01-01-2016 |     3
+(3 rows)
+
 DROP TABLE multi_append_table_to_shard_stage;
 DROP TABLE multi_append_table_to_shard_date;