go.tools/dashboard/builder: use $home on Plan 9
go.tools/dashboard/builder: use $home on Plan 9

LGTM=alex.brainman
R=golang-codereviews, lucio.dere, alex.brainman
CC=golang-codereviews
https://codereview.appspot.com/64520043

skyportsystems/go.tools,8limbs/gotools,webfd/go-zh.tools,skyportsystems/go.tools,skyportsystems/go.tools,bryanxu/go-zh.tools,d0f/go-zh.tools,webfd/go-zh.tools,webfd/go-zh.tools,skyportsystems/go.tools,bryanxu/go-zh.tools,webfd/go-zh.tools,d0f/go-zh.tools,skyportsystems/go.tools,bryanxu/go-zh.tools,8limbs/gotools,bryanxu/go-zh.tools,d0f/go-zh.tools,d0f/go-zh.tools,8limbs/gotools,webfd/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools