Add support for Swift-on-File (SoF).
Add support for Swift-on-File (SoF).

We need a bit of adoption as the SoF DiskFile does not deliver the real file
path for the object.
SoF is currently auto-detected as it uses a symlink in the device directory.
We follow that symlink and append a/c/o to determine the object file path.

ibm-research/SwiftHLM