Currently it is not possible in the Swift Backup Driver
used in single_user mode to connect to Swift in Auth
Version 3. The needed information user_domain,
project_domain and project are not available. This patch
adds the config parameters backup_swift_user_domain,
backup_swift_project_domain and backup_swift_project and
forwards it to the swift client in the os_options parameter.
Adds also the unit test test_backup_swift_auth_v3_single_user
for testing the new configuration parameters.
DocImpact: The config options "backup_swift_user_domain",
"backup_swift_project_domain" and "backup_swift_project"
will need to be added to the Cinder docs. The config option
"backup_swift_auth_version" should reference also version 3.
Closes-Bug: #1518213
Change-Id: Ia57c8b0522f566690a18c8d895ef7db21a558028
