Add clang-format 7.0.1 to CI image (VowpalWabbit#1719)

* Make Dockerfile build again

* Download clang-format

.pipelines/Dockerfile

@@ -1,8 +1,7 @@
 FROM ubuntu:14.04 AS build
 
 # Upgrade cmake to 3.2
-RUN apt-get update
-RUN apt-get install -y software-properties-common python-software-properties debconf-utils
+RUN apt-get update && apt-get install -y software-properties-common python-software-properties debconf-utils
 RUN add-apt-repository -y ppa:george-edison55/cmake-3.x
 RUN apt-get update
 
@@ -62,3 +61,9 @@ RUN apt-get clean autoclean && \
 # Set environment variables used by build
 ENV LD_LIBRARY_PATH="${LD_LIBRARY_PATH}:/usr/local/lib"
 ENV JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64/"
+
+# Download clang-format 7.0
+RUN wget http://releases.llvm.org/7.0.1/clang+llvm-7.0.1-x86_64-linux-gnu-ubuntu-14.04.tar.xz && \
+	tar xvf clang+llvm-7.0.1-x86_64-linux-gnu-ubuntu-14.04.tar.xz && \
+	mv clang+llvm-7.0.1-x86_64-linux-gnu-ubuntu-14.04/bin/clang-format /usr/local/bin && \
+	rm -rf clang+llvm-7.0.1-x86_64-linux-gnu-ubuntu-14.04/