Feature: Dump RDS config from opsworks in .deploy_configuration

Dump Hostname, Username, etc from the Opsworks Recources Database Config in `.deploy_configuration` if set.

Stack JSON
```
{
    "deploy": {
        "appname": {
            "database": {
                "data_source_provider": "rds",
                "database": "dbname",
                "host": "whatever.us-east-1.rds.amazonaws.com",
                "password": "password",
                "port": 3306,
                "reconnect": true,
                "type": "mysql",
                "username": "username"
            }
       }
  }
}
```
will end up in `.deploy_configuration`, prefixed with `AWS_DB_`, e.g. 
 
```
AWS_DB_USERNAME = "username"
AWS_DB_PASSWORD = "password"
AWS_DB_HOST = "whatever.us-east-1.rds.amazonaws.com"
 ...
```