Added option --swift-account in addition to --os-project-id for accessing Swift. This is because Swift API makes use of URL format /v1/{account}/{container}/{object}. When Keystone auth is configured for Swift, which is usually the case, the {account} part is AUTH_{os_project_id}. In the case that another auth system is configured, users need a Swift account to access Swift. Davix should be able to support this scenario as well.