add dbutil.upgrade_if_needed

so it's reusable now that we want to use it in more than one place

jupyterhub/orm.py

@@ -24,7 +24,6 @@ from sqlalchemy.pool import StaticPool
 from sqlalchemy.sql.expression import bindparam
 from sqlalchemy import create_engine, Table
 
-from .dbutil import _temp_alembic_ini
 from .utils import (
     random_port,
     new_token, hash_token, compare_token,
@@ -463,6 +462,8 @@ def check_db_revision(engine):
     current_table_names = set(engine.table_names())
     my_table_names = set(Base.metadata.tables.keys())
 
+    from .dbutil import _temp_alembic_ini
+
     with _temp_alembic_ini(engine.url) as ini:
         cfg = alembic.config.Config(ini)
         scripts = ScriptDirectory.from_config(cfg)