go.crypto/ssh: build test_unix_test on Plan 9
go.crypto/ssh: build test_unix_test on Plan 9

LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://codereview.appspot.com/86630043

xman1101/terminal,drhax9908/go.crypto,drhax9908/go.crypto,xman1101/terminal