AWSCredentialsProvider for s3-extentions

- fileSessionCredentials property is added
- AWSSessionCredentialsAdapter is adapter class between aws sdk AWSCredentialsProvider to jets3t Credentials
- FileSessionCredentialsProvider will refresh its session credentials from the file
- S3StorageDruidModule should return different AWSCredentialsProvider on the config settings
it seems like you only need the credentials to be stored and not the entire provider