Add Helm binary to load tester image

Dockerfile.loadtester

@@ -21,6 +21,10 @@ WORKDIR /home/app
 RUN curl -sSLo hey "https://storage.googleapis.com/jblabs/dist/hey_linux_v0.1.2" && \
 chmod +x hey && mv hey /usr/local/bin/hey
 
+RUN curl -sSL "https://get.helm.sh/helm-v2.12.3-linux-amd64.tar.gz" | tar xvz && \
+chmod +x linux-amd64/helm && mv linux-amd64/helm /usr/local/bin/helm && \
+rm -rf linux-amd64
+
 COPY --from=builder /go/src/github.com/weaveworks/flagger/loadtester .
 
 RUN chown -R app:app ./