On Windows the File::SEPARATOR ends up being `/` which causes
issues with the new way the path is being extracted from the
vbox information. When on Windows (even with WSL), automatically
convert the path to use common forward slash separator. This
fixes path modifications used for storing guest disks.
The dry run import with VirtualBox 6 no longer provides full paths
for disks. Extract base path from suggested settings file location
and use that to generate full path name using provided disk base
name.