Replace connect and close by a optimized select

Author: kadhikari

source/jormungandr/jormungandr/utils.py

@@ -690,9 +690,8 @@ def can_connect_to_database():
     if hasattr(g, 'can_connect_to_database'):
         return g.can_connect_to_database
     try:
-        engine = models.db.engine
-        connection = engine.connect()
-        connection.close()
+        # Instead of creating a new connection to the database, better to test select on the smallest table.
+        models.db.engine.scalar('select version_num from alembic_version;')
         g.can_connect_to_database = True
     except Exception:
         logging.getLogger(__name__).exception('Connection to database has failed')