add guzzle backoff strategy to client object

add_backoff.php

<?php

// First make sure you have the BackoffPlugin installed:
// $ composer require guzzle/guzzle

use Guzzle\Plugin\Backoff\BackoffPlugin;
use OpenCloud\Rackspace;

$client = new Rackspace(Rackspace::US_IDENTITY_ENDPOINT, array(
  'username' => 'foo',
  'apiKey'   => 'bar'
));

$maxRetries = 5;
$httpCodes = array(503);
$curlCodes = array(50);
$backoff = BackoffPlugin::getExponentialBackoff($maxRetries, $httpCodes, $curlCodes);

$client->addSubscriber($backoff);