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
For local files we might read different permission from the filesystem. Which is why the might be readonly. For the object store the owner of a new file is allowed to do everything with them. @icewind1991 I think this assumption is correct, isn't it.