Fix error of tacker-db-manage postgresql migration

After introducing codes for updating sqlalchemy version 2,
when db is populated to postgresql by running `tacker-db-manage
upgrade head`, `sqlalchemy.table` function raise "NoSuchTable"
error if "engine" is passed as autoload_with.
This patch fix the above error by changing "engine" to "connection".

Closes-bug: #2085879
Change-Id: If14d101ceb510b38d14725ae27b81d9131cd4332

tacker/db/migration/alembic_migrations/versions/0ae5b1ce3024_unique_constraint_name.py

@@ -35,11 +35,10 @@ def _migrate_duplicate_names(table):
 
     meta = sa.MetaData()
     conn = op.get_bind()
-    engine = conn.engine
-    meta.create_all(bind=engine)
-    t = sa.Table(table, meta, autoload_with=engine)
+    meta.create_all(bind=conn)
+    t = sa.Table(table, meta, autoload_with=conn)
 
-    session = sa.orm.Session(bind=engine)
+    session = sa.orm.Session(bind=conn)
     #with session.begin(subtransactions=True):
     with session.begin():
         dup_names = session.query(t.c.name).group_by(

tacker/db/migration/alembic_migrations/versions/6e56d4474b2a_blob_to_json_text.py

@@ -38,9 +38,8 @@ down_revision = 'f958f58e5daa'
 def _migrate_data(table, column_name):
     meta = sa.MetaData()
     conn = op.get_bind()
-    engine = conn.engine
-    meta.create_all(bind=engine)
-    t = sa.Table(table, meta, autoload_with=engine)
+    meta.create_all(bind=conn)
+    t = sa.Table(table, meta, autoload_with=conn)
 
     for r in conn.execute(t.select()):
         stmt = t.update().where(t.c.id == r.id).values(

tacker/db/migration/alembic_migrations/versions/975e28392888_add_unique_key_vnf_package_vnfd.py

@@ -35,11 +35,10 @@ def _migrate_duplicate_vnf_package_vnfd_id(table):
 
     meta = sa.MetaData()
     conn = op.get_bind()
-    engine = conn.engine
-    meta.create_all(bind=engine)
-    t = sa.Table(table, meta, autoload_with=engine)
+    meta.create_all(bind=conn)
+    t = sa.Table(table, meta, autoload_with=conn)
 
-    session = sa.orm.Session(bind=engine)
+    session = sa.orm.Session(bind=conn)
     with session.begin():
         dup_vnfd_ids = session.query(t.c.vnfd_id).group_by(
             t.c.vnfd_id).having(sa.func.count() > 1).all()