[MIG+FIX] base_comment_template: Fix migration scripts

As the field was not properly converted to property at 2.0.0, the script fails to do its
job when migrating from v11, so we need to adapt the scripts to this situation.

base_comment_template/migrations/12.0.2.0.0/pre-migration.py

@@ -0,0 +1,13 @@
+# Copyright 2020 Tecnativa - Pedro M. Baeza
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+from openupgradelib import openupgrade
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    cr = env.cr
+    table = 'res_partner'
+    old_column = 'comment_template_id'
+    new_column = 'property_comment_template_id'
+    if openupgrade.column_exists(cr, table, old_column):
+        openupgrade.rename_columns(cr, {table: [(old_column, new_column)]})