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://codereview.appspot.com/138140043

karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools