Add default value for enabled column in l7rule table

we don't set default value for enabled column now,
and mysql will fill them with 0 value(false)
if we upgrade from ocata or ealier, all l7rules is disabled.
so they will not render to haproxy config file in amphora.
this will cause all l7rules  stop work after a update.

Change-Id: Ib8549d71b7adb95d0dcb36903c1744190056adae

octavia/db/migration/alembic_migrations/versions/b8bd389cbae7_update_default_value_in_l7rule_table.py

@@ -0,0 +1,37 @@
+# Copyright 2020 Yovole
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+#
+
+"""update default value in l7rule table
+
+Revision ID: b8bd389cbae7
+Revises: 8b47b2546312
+Create Date: 2020-12-03 13:40:00.520336
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = 'b8bd389cbae7'
+down_revision = 'be9fdc039b51'
+
+
+def upgrade():
+    op.alter_column(
+        'l7rule',
+        'enabled',
+        existing_nullable=False,
+        server_default=sa.sql.expression.true())

octavia/db/migration/alembic_migrations/versions/d85ca7258d21_modernize_l7rule.py

@@ -50,7 +50,9 @@ def upgrade():
     # Add enabled
     op.add_column(
         u'l7rule',
-        sa.Column(u'enabled', sa.Boolean(), nullable=False)
+        sa.Column(u'enabled', sa.Boolean(),
+                  server_default=sa.sql.expression.true(),
+                  nullable=False)
     )
 
     # Add new operating_status column, setting existing rows to ONLINE