Add a delay at the start of the stats test, to let any prior stats

activity quiesce.  Possibly this will fix the large increase in
non-reproducible stats test failures we've noted since turning on
stats_row_level by default.

src/test/regress/expected/stats.out

@@ -11,6 +11,14 @@ SHOW stats_start_collector;  -- must be on
  on
 (1 row)
 
+-- wait to let any prior tests finish dumping out stats;
+-- else our messages might get lost due to contention
+SELECT pg_sleep(2.0);
+ pg_sleep 
+----------
+ 
+(1 row)
+
 -- save counters
 CREATE TEMP TABLE prevstats AS
 SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,

src/test/regress/sql/stats.sql

@@ -8,6 +8,10 @@
 -- conditio sine qua non
 SHOW stats_start_collector;  -- must be on
 
+-- wait to let any prior tests finish dumping out stats;
+-- else our messages might get lost due to contention
+SELECT pg_sleep(2.0);
+
 -- save counters
 CREATE TEMP TABLE prevstats AS
 SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,