go.crypto/ssh: fix test breakage
go.crypto/ssh: fix test breakage

Followup CL for 9711043. The order that CombinedOutput returns data captured from stdout/stderr is not specified, so we have to test both variants.

Thanks to fullung for the bug report.

R=fullung, kr
CC=golang-dev
https://golang.org/cl/9921044

pki-io/crypto,cheffo/crypto,cmars/tools,ScriptRock/crypto,kim-racktop/crypto,conseweb/golangcrypto,juniorz/crypto,guaiguaihw/crypto,golang/crypto,tca/crypto,golang/crypto,golang/crypto,mattharden/crypto,lucevers/crypto,CodyGuo/crypto,mattharden/crypto,cmars/tools,progrium/crypto,cheffo/crypto,a-palchikov/crypto,bford/golang-x-crypto,thomaso-mirodin/crypto,a-palchikov/crypto,zj8487/crypto,pki-io/crypto,lucevers/crypto,conseweb/golangcrypto,wooutl/golangcrypto,Carrotman42/crypto,CodyGuo/crypto,Carrotman42/crypto,juniorz/crypto,cmars/tools,guaiguaihw/crypto,ScriptRock/crypto,zj8487/crypto,bford/golang-x-crypto,kim-racktop/crypto,tca/crypto,wooutl/golangcrypto,cmars/tools,thomaso-mirodin/crypto,progrium/crypto