Use prebuilt container with jsonnet in it

scripts/jsonnet/Dockerfile

@@ -1,18 +0,0 @@
-FROM golang:1.12-stretch
-
-ENV JSONNET_VERSION 0.12.1
-
-RUN apt-get update -y && apt-get install -y jq && rm -rf /var/lib/apt/lists/*
-RUN curl -Lso - https://github.com/google/jsonnet/archive/v${JSONNET_VERSION}.tar.gz | \
-    tar xfz - -C /tmp && \
-    cd /tmp/jsonnet-${JSONNET_VERSION} && \
-    make && mv jsonnet /usr/local/bin && \
-    rm -rf /tmp/jsonnet-${JSONNET_VERSION}
-RUN go get github.com/brancz/gojsontoyaml
-RUN go get github.com/campoy/embedmd
-RUN go get github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb
-
-RUN mkdir -p /go/src/github.com/coreos/kube-prometheus
-WORKDIR /go/src/github.com/coreos/kube-prometheus
-
-RUN chmod -R 777 /go