go.tools/dashboard/builder: rewrite sub-repo paths before 'go get' and 'go test'
go.tools/dashboard/builder: rewrite sub-repo paths before 'go get' and 'go test'

The dashboard still uses the old "code.google.com/p/go.*" import paths.
Rewrite them to the new "golang.org/x/*" before running 'go get' and 'go test'.

Update golang/go#9079.

LGTM=rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/174740043

cmars/tools,jdhenke/tools,cmars/tools,golang/tools,golang/tools,argandas/tools,syreclabs/go-tools,springning/tools,glasser/golang-tools,4ad/tools,dmitris/tools,cw2018/tools,cmars/tools,josharian/tools,jdhenke/tools,4ad/tools,cmars/tools,runcom/tools,runcom/tools,nicot/tools,4ad/tools,josharian/tools,argandas/tools,syreclabs/go-tools,sshetty10/tools,sshetty10/tools,nicot/tools,maddyonline/tools,golang/tools,runcom/tools,matryer/tools,nicot/tools,cw2018/tools,jdhenke/tools,springning/tools,matryer/tools,springning/tools,dmitris/tools,runcom/tools,matryer/tools,magiccao/tools,syreclabs/go-tools,maddyonline/tools,magiccao/tools,jdhenke/tools,sshetty10/tools,springning/tools,argandas/tools,maddyonline/tools,josharian/tools,syreclabs/go-tools,cw2018/tools,glasser/golang-tools,magiccao/tools,dmitris/tools,dmitris/tools,matryer/tools,golang/tools,sshetty10/tools,magiccao/tools,argandas/tools,nicot/tools,josharian/tools,syreclabs/go-tools,golang/tools,glasser/golang-tools,syreclabs/go-tools,glasser/golang-tools,cw2018/tools,maddyonline/tools