Support OpenStack Swift as a backend

To run test_bakthat_swift.py, a Swift cluster is required.
(It may be better to prepare for mock of swiftclient)

Swift is multi server system, but you can build a clust
with a server by SAIO (Swift All in One).
http://docs.openstack.org/developer/swift/development_saio.html
Merge pull request #15 from yoyama/swift

Support OpenStack Swift as a backend