Improve the selectability of Swift tests

Before this commit, Tempest tests of Swift were selectable only for WSGI
middleware on proxy servers. With this commit, other following Swift
functions are also selectable with Tempest's config file.

Following Swift functions are selectable now:
 - Old-style Container Sync: mirroring objects in the container to another
   container
 - Object Versioning: versioning all objects in the container
 - Discoverability: providing details about the Swift installation

Implements blueprint more-selectable-swift-tests

Change-Id: Idd4afb675c70eea6ba4f8ce59c635f32f040c61e
Merge "Improve the selectability of Swift tests"