Resolve Credentials issues and queue URL issues

[JamesJJ]

• Related to https://github.com/ixixi/fluent-plugin-sqs/issues/39 and https://github.com/ixixi/fluent-plugin-sqs/pull/40, we avoid setting Aws.config because that is shared between all AWS SDK clients in use.

• Related to https://github.com/aws/aws-sdk-ruby/issues/1620, we avoid asking for sqs_url as a configuration option, because depending on the AWS SDK version you have, it may not be able to handle both formats of SQS URL that are in use currently e.g.
  • https://{REGION}.queue.amazonaws.com/{ACCOUNT_ID}/{QUEUE_NAME}
  • https://sqs.{REGION}.amazonaws.com/{ACCOUNT_ID}/{QUEUE_NAME}