dashboard/builder: add -report=false flag for testing Docker images
dashboard/builder: add -report=false flag for testing Docker images

LGTM=proppy
R=proppy
CC=golang-codereviews
https://golang.org/cl/138140043

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