Fix build

Install the dependencies directly into the build container rather than
at runtime. This will keep the build more stable than relying on master.

Author: csmarchbanks

.circleci/Dockerfile

@@ -7,5 +7,9 @@ RUN git clone https://github.com/google/jsonnet && \
     git  -C jsonnet checkout v0.12.1 && \
     make -C jsonnet LDFLAGS=-static
 
+FROM prom/prometheus:v2.8.1
+
 FROM circleci/golang:1.10.3-stretch
 COPY --from=0 jsonnet/jsonnet /usr/bin
+COPY --from=1 /bin/promtool /usr/bin
+RUN go get github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb

.circleci/config.yml

@@ -2,15 +2,10 @@ version: 2
 jobs:
   build:
     docker:
-      - image: csmarchbanks/kubernetes-mixin-build:jsonnet-0.12.1
+      - image: csmarchbanks/kubernetes-mixin-build:0.1.1
 
     working_directory: /go/src/github.com/kubernetes-monitoring/kubernetes-mixin
     steps:
       - checkout
-      - run:
-          name: Install tools
-          command: |
-            go get github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb
-            go get github.com/prometheus/prometheus/cmd/promtool
       - run: jb install
       - run: make