[bug 889271] Fix migration 226

This adds the missing product that migration 226 balks at plus
adds a note to migration 226 about how to add products in the future if
it dies again.

To test:

1. change the database name in your settings_local.py to something like "kitsuneblank"
2. run: `mysql kitsuneblank < scripts/schema.sql`
3. run: `./vendor/src/schematic/schematic migrations/`

It should go through all the migrations.

I wrote a fab rule so I can trivially test migrations on a blank db. I'll try to do that for new migrations so we don't bump into this again.

r?