Fix flaky test in recoverseg_from_file

1. after stop primary with content=1, we should check promotion
status with 1U:
2. after manually update dbid, we should trigger a fts probe and
wait for the mirror promotion as well.

src/test/isolation2/expected/segwalrep/recoverseg_from_file.out

@@ -43,21 +43,38 @@ select gp_request_fts_probe_scan();
  t                         
 (1 row)
 
--- wait for content 0 (earlier mirror, now primary) to finish the promotion
-0U: select 1;
+-- wait for content 1 (earlier mirror, now primary) to finish the promotion
+1U: select 1;
  ?column? 
 ----------
  1        
 (1 row)
 -- Quit this utility mode session, as need to start fresh one below
-0Uq: ... <quitting>
+1Uq: ... <quitting>
 
 -- make the dbid in gp_segment_configuration not continuous
+-- dbid=2 corresponds to content id =0
 set allow_system_table_mods to true;
 SET
 update gp_segment_configuration set dbid=9 where dbid=2;
 UPDATE 1
 
+-- trigger failover
+select gp_request_fts_probe_scan();
+ gp_request_fts_probe_scan 
+---------------------------
+ t                         
+(1 row)
+
+-- wait for content 0 (earlier mirror, now primary) to finish the promotion
+0U: select 1;
+ ?column? 
+----------
+ 1        
+(1 row)
+-- Quit this utility mode session, as need to start fresh one below
+0Uq: ... <quitting>
+
 -- generate recover config file
 select generate_recover_config_file( (select datadir from gp_segment_configuration c where c.role='m' and c.content=1), (select port from gp_segment_configuration c where c.role='m' and c.content=1)::text);
  generate_recover_config_file 
@@ -65,7 +82,7 @@ select generate_recover_config_file( (select datadir from gp_segment_configurati
                               
 (1 row)
 
--- recover from config file
+-- recover from config file, only seg with content=1 will be recovered
 !\retcode gprecoverseg -a -i /tmp/recover_config_file;
 -- start_ignore
 -- end_ignore

src/test/isolation2/sql/segwalrep/recoverseg_from_file.sql

@@ -34,21 +34,30 @@ where c.role='p' and c.content=1), 'stop');
 -- trigger failover
 select gp_request_fts_probe_scan();
 
--- wait for content 0 (earlier mirror, now primary) to finish the promotion
-0U: select 1;
+-- wait for content 1 (earlier mirror, now primary) to finish the promotion
+1U: select 1;
 -- Quit this utility mode session, as need to start fresh one below
-0Uq:
+1Uq:
 
 -- make the dbid in gp_segment_configuration not continuous
+-- dbid=2 corresponds to content id =0
 set allow_system_table_mods to true;
 update gp_segment_configuration set dbid=9 where dbid=2;
 
+-- trigger failover
+select gp_request_fts_probe_scan();
+
+-- wait for content 0 (earlier mirror, now primary) to finish the promotion
+0U: select 1;
+-- Quit this utility mode session, as need to start fresh one below
+0Uq:
+
 -- generate recover config file
 select generate_recover_config_file(
 	(select datadir from gp_segment_configuration c where c.role='m' and c.content=1),
 	(select port from gp_segment_configuration c where c.role='m' and c.content=1)::text);
 
--- recover from config file
+-- recover from config file, only seg with content=1 will be recovered
 !\retcode gprecoverseg -a -i /tmp/recover_config_file;
 
 -- after gprecoverseg -i, the down segemnt should be up