Add alternate expected output for pg_buffercache with 4-node cluster

Update expected output to match standard demo cluster with 1
coordinator + 3 primaries: gp_buffercache_summary returns 4 rows
and buffer count matches shared_buffers * primary_count.

Author: lss602726449

contrib/pg_buffercache/expected/pg_buffercache.out

@@ -50,7 +50,7 @@ SELECT count(*) = (select setting::bigint
 FROM gp_buffercache;
  buffers 
 ---------
- f
+ t
 (1 row)
 
 SELECT buffers_used + buffers_unused > 0,
@@ -61,7 +61,9 @@ FROM gp_buffercache_summary;
 ----------+----------+----------
  t        | t        | t
  t        | t        | t
-(2 rows)
+ t        | t        | t
+ t        | t        | t
+(4 rows)
 
 SELECT buffers_used + buffers_unused > 0,
         buffers_dirty <= buffers_used,
@@ -146,7 +148,9 @@ SELECT buffers_used + buffers_unused > 0 FROM gp_buffercache_summary;
 ----------
  t
  t
-(2 rows)
+ t
+ t
+(4 rows)
 
 SELECT buffers_used + buffers_unused > 0 FROM gp_buffercache_summary_aggregated;
  ?column?