Don't hardcode contrib_regression dbname in postgres_fdw and dblink tests.

That allows parallel installcheck to succeed inside contrib/. The
output is not particularly pretty unless make's -O option to
synchronize the output is used.

There's other tests, outside contrib, that use a hardcoded,
non-unique, database name. Those prohibit paralell installcheck to be
used across more directories; but that's something for a separate
patch.

contrib/postgres_fdw/Makefile

@@ -13,9 +13,6 @@ DATA = postgres_fdw--1.0.sql
 
 REGRESS = postgres_fdw
 
-# the db name is hard-coded in the tests
-override USE_MODULE_DB =
-
 ifdef USE_PGXS
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -3,8 +3,12 @@
 -- ===================================================================
 CREATE EXTENSION postgres_fdw;
 CREATE SERVER testserver1 FOREIGN DATA WRAPPER postgres_fdw;
-CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
-  OPTIONS (dbname 'contrib_regression');
+DO $d$
+    BEGIN
+        EXECUTE $$CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
+            OPTIONS (dbname '$$||current_database()||$$');$$;
+    END;
+$d$;
 CREATE USER MAPPING FOR public SERVER testserver1
 	OPTIONS (user 'value', password 'value');
 CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -5,8 +5,12 @@
 CREATE EXTENSION postgres_fdw;
 
 CREATE SERVER testserver1 FOREIGN DATA WRAPPER postgres_fdw;
-CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
-  OPTIONS (dbname 'contrib_regression');
+DO $d$
+    BEGIN
+        EXECUTE $$CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
+            OPTIONS (dbname '$$||current_database()||$$');$$;
+    END;
+$d$;
 
 CREATE USER MAPPING FOR public SERVER testserver1
 	OPTIONS (user 'value', password 'value');