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

evandbrown/build,evandbrown/build,golang/build,golang/build,golang/build,proppy/build,proppy/build,evandbrown/build,proppy/build,golang/build,proppy/build