OpenStack Swift storage driver

An implementation of the storagedriver.StorageDriver interface that uses OpenStack Swift for object storage.

Parameters

`authurl`	URL for obtaining an auth token.
`username`	Your OpenStack user name.
`password`	Your OpenStack password.
`container`	The name of your Swift container where you wish to store objects. An additional container called `_segments` stores the data is used. The driver creates both the named container and the segments container during its initialization.
`tenant`	Optionally, your OpenStack tenant name. You can either use `tenant` or `tenantid`.
`tenantid`	Optionally, your OpenStack tenant id. You can either use `tenant` or `tenantid`.
`domain`	Optionally, your OpenStack domain name for Identity v3 API. You can either use `domain` or `domainid`.
`domainid`	Optionally, your OpenStack domain id for Identity v3 API. You can either use `domain` or `domainid`.
`insecureskipverify`	Optionally, set `insecureskipverify` to true to skip TLS verification for your OpenStack provider. The driver uses false by default.
`region`	Optionally, specify the OpenStack region name in which you would like to store objects (for example `fr`).
`chunksize`	Optionally, specify the segment size for Dynamic Large Objects uploads (performed by WriteStream) to Swift. The default is 5 MB. You might experience better performance for larger chunk sizes depending on the speed of your connection to Swift.
`prefix`	Optionally, supply the root directory tree in which to store all registry files. Defaults to the empty string which is the container's root.