os: re-enable hostname test on openbsd
os: re-enable hostname test on openbsd

Now that Sysctl() works, re-enable the hostname test.

R=golang-dev, mikioh.mikioh
CC=golang-dev
http://codereview.appspot.com/5408042
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go