Strengthen the pattern to find auxiliary tables by name

The privious pattern used by the test was not strong enough.  It could
accidentally matched names of partitioned tables.  Name of a partition
being added is generated by suffixing a random number, if no name is
specified by the user.  E.g. "sales_1_prt_r1171829080_2_prt_usa".  At
least one time, the test failed CI due to this weakness.

The new pattern is strong enough to match only the auxiliary table
names that end with "_<oid>".

Reviewed by Heikki and Georgios.

src/test/regress/expected/freeze_aux_tables.out

@@ -37,7 +37,7 @@ begin
   for rec in select gp_segment_id, replace(relname, testrelid::oid::text, '<oid>'), age(relfrozenxid)
     from pg_class
     where relkind in ('r','t','o','b','M') and relstorage not in ('x','f','v')
-    and (relname like '%' || testrelid::oid || '%' or oid = testrelid::oid )
+    and (relname like '%\_' || testrelid::oid or oid = testrelid::oid )
     and not relfrozenxid = 0
   loop
     return next rec;
@@ -46,7 +46,7 @@ begin
   for rec in select gp_segment_id, replace(relname, testrelid::oid::text, '<oid>'), age(relfrozenxid)
     from gp_dist_random('pg_class')
     where relkind in ('r','t','o','b','M') and relstorage not in ('x','f','v')
-    and (relname like '%' || testrelid::oid || '%' or oid = testrelid::oid )
+    and (relname like '%\_' || testrelid::oid or oid = testrelid::oid )
     and not relfrozenxid = 0
   loop
     return next rec;

src/test/regress/sql/freeze_aux_tables.sql

@@ -43,7 +43,7 @@ begin
   for rec in select gp_segment_id, replace(relname, testrelid::oid::text, '<oid>'), age(relfrozenxid)
     from pg_class
     where relkind in ('r','t','o','b','M') and relstorage not in ('x','f','v')
-    and (relname like '%' || testrelid::oid || '%' or oid = testrelid::oid )
+    and (relname like '%\_' || testrelid::oid or oid = testrelid::oid )
     and not relfrozenxid = 0
   loop
     return next rec;
@@ -52,7 +52,7 @@ begin
   for rec in select gp_segment_id, replace(relname, testrelid::oid::text, '<oid>'), age(relfrozenxid)
     from gp_dist_random('pg_class')
     where relkind in ('r','t','o','b','M') and relstorage not in ('x','f','v')
-    and (relname like '%' || testrelid::oid || '%' or oid = testrelid::oid )
+    and (relname like '%\_' || testrelid::oid or oid = testrelid::oid )
     and not relfrozenxid = 0
   loop
     return next rec;