[RFC] Fix functional-test-105 failure in OSX.

See https://github.com/neovim/neovim/issues/1519 for failure report.
```
Cause    : In OSX, /tmp is a symbolic link to /private/tmp, which causes
           expected and got results different because of implicit
           resolution.
Solution : Resolve path before setting expected value.
```
Fixes #1519.