CreateFile ioctl does not appear to respect `SetPreferredTargets()`

[iamjoemccormick]

As part of #221 I added the ability to migrate files to specific targets and groups. While implementing this I noticed the CreateFile() ioctl's SetPreferredTargets option does not seem to have any effect. I'm not sure if this is a bug with the Go ioctl library or the client ioctl handling.

We need that ioctl to migrate symlinks using temporary files. Once this bug is resolved, enable the ability to migrate symlinks to specific targets/groups in tempFileMigrateLink().