Wait until RDS snapshot has been restored on initial install before trying to create DB tables too early

When deploying using the CloudFormation template, when restoring a database from a snapshot it is possible that the authserver and worldserver EC2 instances connect to the database before it has restored from a snapshot. In this event, brand new and empty tables will be created which will prevent the snapshot from being restoreing.

A couple of options:

Investigate the use of RDS SNS event notifications so that the EC2 instances have to wait for a db-snapshot/restoration or db-instance/restoration and db-instance/availability event perhaps?

• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_Events.html
• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_Events.Subscribing.html
• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_Events.ListingCategories.html

Alternatively, the CFN init scripts and wait-for-mysql.sh helper in the container could be extended to wait for the existence of an arbitrary list of databases to appear on the RDS server (characters, auth and world) before proceeding when we are restoring from a snapshot.