Added build constraint to home_unix test file.

Without this build constraint, a naming conflict would arise between the suites for the two platforms on Windows as _unix is not recognized by the go compiler as a valid build constraint, resulting in the tests failing to build.
Anyhow, the home_unix tests never had a chance in working on Windows in the first place as home_unix itself has the same build constraint.

Special thanks to @howbazaar for the suggestion.