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>

pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,h8liu/golang,ssrl/go,tv42/old-go,apparentlymart/golang,dsriram/golang,dsriram/golang,ssrl/go,gnanderson/go,ssrl/go,dsriram/golang,tv42/old-go,apparentlymart/golang,h8liu/golang,h8liu/golang,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,ssrl/go,gnanderson/go,h8liu/golang,gnanderson/go,apparentlymart/golang,dsriram/golang,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,h8liu/golang,apparentlymart/golang,h8liu/golang,apparentlymart/golang,gnanderson/go,h8liu/golang,dsriram/golang,apparentlymart/golang,ssrl/go,pombredanne/go-deleteme,tv42/old-go,ssrl/go,dsriram/golang,gnanderson/go,ssrl/go