ghbot should only respond to repos in its database

[millerh1]

To prevent double-posting during development / testing, the ghbot should be modified so that it can only respond to messages in repos which it already has in its database. This will prevent the production bot from responding to repos made during local development / testing.

However, it may also be important to prevent the development database from having a copy of open repos in production database. The reason is that the local bot may start responding to trainee activity in addition to the production bot.