os: Use TempFile with default TempDir for temp test files
os: Use TempFile with default TempDir for temp test files

Use io/ioutil.TempFile with default os.TempDir for temporary test files.
For os_test.go temporary test files, use a local file system and OS
independent directory names. Avoid problems with NFS.

Fixes issue 848.

R=adg
CC=golang-dev
http://codereview.appspot.com/1806043

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go