Close database after initialization of Pool from WSGI application

The psycopg pool starts worker threads that must be stopped.

Closes #14849

trytond/trytond/application.py

@@ -31,11 +31,16 @@ Pool.start()
 # TRYTOND_CONFIG it's managed by importing config
 db_names = os.environ.get('TRYTOND_DATABASE_NAMES')
 if db_names:
+    from trytond import backend
+
+    def initializer(name):
+        Pool(name).init()
+        backend.Database(name).close()
     # Read with csv so database name can include special chars
     reader = csv.reader(StringIO(db_names))
     threads = []
     for name in next(reader):
-        thread = threading.Thread(target=lambda: Pool(name).init())
+        thread = threading.Thread(target=initializer, args=(name,))
         thread.start()
         threads.append(thread)
     for thread in threads:

trytond/trytond/backend/postgresql/database.py

@@ -286,7 +286,7 @@ class Database(DatabaseInterface):
     def close(self):
         with self._lock:
             logger.info('disconnection from "%s"', self.name)
-            self._connpool.close()
+            self._connpool.close(None)
             self._databases[os.getpid()].pop(self.name)
 
     @classmethod