Install buildifier utility

Buildifier is a tool for formatting bazel BUILD files with a standard
convention. Once installed, the formatting of BUILD files can be
evaluated as following:

  $ buildifier -showlog -mode=check $(find . -name BUILD -o -name \
WORKSPACE -type f)

Change-Id: I3e0270a8cf6e3aba2ca615421cc868f525ea83a0
diff --git a/jenkins-docker/slave-bazel/Dockerfile b/jenkins-docker/slave-bazel/Dockerfile
index ed4dc63..8159e4a 100644
--- a/jenkins-docker/slave-bazel/Dockerfile
+++ b/jenkins-docker/slave-bazel/Dockerfile
@@ -7,6 +7,14 @@
 RUN apt-get update && apt-get install -y bazel \
     && rm -rf /var/lib/apt/lists/*
 
+# Install buildifier utility
+ADD https://storage.googleapis.com/golang/go1.8.3.linux-amd64.tar.gz /tmp/golang.tar.gz
+RUN cd /usr/local && \
+    tar xvfz /tmp/golang.tar.gz && \
+    cd /usr/local/bin && \
+    ln -s /usr/local/go/bin/* . && \
+    go get github.com/bazelbuild/buildtools/buildifier
+
 # Bazel cache warm-up with Gerrit master build
 USER jenkins
 RUN bash -c '. /usr/bin/set-java.sh 8 && \