Use just one database connection in the "tablespace" test.

On Windows, DROP TABLESPACE has a race condition when run concurrently
with other processes having opened files in the tablespace.  This led to
a rare failure on buildfarm member frogmouth.  Back-patch to 9.4, where
the reconnection was introduced.

src/backend/commands/tablespace.c

@@ -493,6 +493,13 @@ DropTableSpace(DropTableSpaceStmt *stmt)
 		 * but we can't tell them apart from important data files that we
 		 * mustn't delete.  So instead, we force a checkpoint which will clean
 		 * out any lingering files, and try again.
+		 *
+		 * XXX On Windows, an unlinked file persists in the directory listing
+		 * until no process retains an open handle for the file.  The DDL
+		 * commands that schedule files for unlink send invalidation messages
+		 * directing other PostgreSQL processes to close the files.  DROP
+		 * TABLESPACE should not give up on the tablespace becoming empty
+		 * until all relevant invalidation processing is complete.
 		 */
 		RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
 		if (!destroy_tablespace_directories(tablespaceoid, false))

src/test/regress/input/tablespace.source

@@ -71,8 +71,7 @@ ALTER TABLESPACE testspace OWNER TO tablespace_testuser1;
 
 SET SESSION ROLE tablespace_testuser2;
 CREATE TABLE tablespace_table (i int) TABLESPACE testspace; -- fail
-
-\c -
+RESET ROLE;
 
 ALTER TABLESPACE testspace RENAME TO testspace_renamed;
 

src/test/regress/output/tablespace.source

@@ -91,7 +91,7 @@ ALTER TABLESPACE testspace OWNER TO tablespace_testuser1;
 SET SESSION ROLE tablespace_testuser2;
 CREATE TABLE tablespace_table (i int) TABLESPACE testspace; -- fail
 ERROR:  permission denied for tablespace testspace
-\c -
+RESET ROLE;
 ALTER TABLESPACE testspace RENAME TO testspace_renamed;
 ALTER TABLE ALL IN TABLESPACE testspace_renamed SET TABLESPACE pg_default;
 ALTER INDEX ALL IN TABLESPACE testspace_renamed SET TABLESPACE pg_default;