add rackspace and update composer

This PR adds the rackspace libraries necessary for the objectstore swift implementation in core.
I added `"rackspace/php-opencloud": "v1.9.2"` to composer.json but it had problems updating a repo. Likely because an update did not check in the code as well. So I ran `php composer.phar update` and added all changed files.

prerequisite for https://github.com/owncloud/core/pull/8383