Early versions of Aurora used just "aurora" as the value for the engine parameter. But Aurora now supports more than one database, so the engine string has been updated to, as of this writing, support aurora-mysql and aurora-postgres.
Without this change, it's impossible to use this method to create individual aurora instances because the code fog forces the caller to specify the master_username, password, and allocated_storage values. None of which are valid for Aurora instances.
I also updated the default "flavor_id" values to more recent versions since db.m1s don't exist anymore, and db.r3s are being phased out.
* add db cluster identifier to db instance parser
* dont allow setting security groups on aurora instances
* aurora instances do not support the multi az parameter due to the cluster
* aurora has its own storage type that cannot be set
* add mock
* add restore method on servers collection
* modify save method on server model
* raise error when multi_az and az are set
* cannot specify multi_az to be true and pick an az together
* take allocated_storage from snapshot on restore
* restore from snapshot endpoint does not take
* allocated_storage parameter
* save storage type on rds snapshot
