cmd/godoc: godoc test needs clean up tmp dir when buildGodoc fails.
cmd/godoc: godoc test needs clean up tmp dir when buildGodoc fails.

Change-Id: I584ed27d37a85d39294b07febf396f567d4016a5
Reviewed-on: https://go-review.googlesource.com/2901
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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