Add and check data functions for test_migrations 141

Before the 141 migration test is run, _prerun_141 populates the migrations
table with a generated uuid. The _check_141 function checks that
the uuid migrated properly down to 36 char.

Partially implements: blueprint migration-testing-with-data

Change-Id: I43b47f69a94720bf9487eb30576035493700ddca

nova/tests/test_migrations.py

@@ -47,6 +47,7 @@ import datetime
 import os
 import sqlalchemy
 import urlparse
+import uuid
 
 from migrate.versioning import repository
 
@@ -440,6 +441,24 @@ class TestMigrations(BaseMigrationTestCase):
 
         self.assertEqual(data[0]['mac'], bw['mac'])
 
+    # migration 141, update migrations instance uuid
+    def _prerun_141(self, engine):
+        data = {
+            'instance_uuid': str(uuid.uuid4())
+            }
+        migrations = get_table(engine, 'migrations')
+        engine.execute(migrations.insert(), data)
+        result = migrations.insert().values(data).execute()
+        data['id'] = result.inserted_primary_key[0]
+        return data
+
+    def _check_141(self, engine, data):
+        migrations = get_table(engine, 'migrations')
+        row = migrations.select(
+            migrations.c.id == data['id']).execute().first()
+        # Check that change to String(36) went alright
+        self.assertEqual(data['instance_uuid'], row['instance_uuid'])
+
     # migration 146, availability zone transition
     def _prerun_146(self, engine):
         data = {