Object storage

don't merge before https://github.com/owncloud/3rdparty/pull/99 is in 3rdparty
- [ ] https://github.com/owncloud/3rdparty/pull/99 moves rackspace to 3rdparty, but files_external also provides it, causing tests to fail ...
- [x] swift test should create a new container on every test run and delete it afterwards
Any reason why you don't inherit the generic Storage test case here?

(i.e. https://github.com/owncloud/core/blob/master/tests/lib/files/storage/local.php#L25)