Fix database detection in rails cookbook

As for version 330 of opsworks agent database type reported as 'type', when rails::configure expects 'adapter'.
Because of this bug - there is no way to use rails and postgres rds, database.yml always overridden and it always got wrong adapter type.

```bash
root@cumulonimbus:/opt/aws/opsworks/current/bin# ./opsworks-agent-cli agent_report

AWS OpsWorks Instance Agent State Report:

  Last activity was a "configure" on 2014-11-24 03:49:19 UTC
  Agent Status: The AWS OpsWorks agent is running as PID 17661
  Agent Version: 330, up to date
```
```json
root@cumulonimbus:/opt/aws/opsworks/current/bin# ./opsworks-agent-cli get_json | grep -A7 'database\":'
      "database": {
        "host": "*****************************************",
        "database": "************",
        "port": 5432,
        "username": "*****",
        "password": "**********************",
        "reconnect": true,
        "data_source_provider": "rds",
        "type": "postgresql"
      }
```