Execute attach_time query earlier in migration 98

MySQL was blowing up when sqlalchemy tried to execute the subqueries
in up/downgrade for migration 98. SQLite wasn't blowing up on this so
the tests were passing in Jenkins.

There are no test changes as it depends on the functional environment
in which you run the tests, not the tests themselves.

Fixes bug 1047665

Change-Id: I6eb3c8dd03495cdda2574efc9b5fc2b495fbcb37

nova/db/sqlalchemy/migrate_repo/versions/098_update_volume_attach_time.py

@@ -32,7 +32,7 @@ def upgrade(migrate_engine):
         volumes_list = list(volumes.select().execute())
         for v in volumes_list:
             attach_time = select([volumes.c.attach_time],
-                volumes.c.id == v['id'])
+                volumes.c.id == v['id']).execute().fetchone()[0]
             volumes.update().\
                 where(volumes.c.id == v['id']).\
                 values(attachtime_datetime=attach_time).execute()
@@ -59,7 +59,7 @@ def downgrade(migrate_engine):
         volumes_list = list(volumes.select().execute())
         for v in volumes_list:
             attach_time = select([volumes.c.attach_time],
-                volumes.c.id == v['id'])
+                volumes.c.id == v['id']).execute().fetchone()[0]
             volumes.update().\
                 where(volumes.c.id == v['id']).\
                 values(attachtime_string=attach_time).execute()