Dockerfile: install packages before copying the directory

This allows Docker to cache the installation of packages.

Dockerfile

@@ -2,22 +2,21 @@
 # build with: docker build -t nativejson-benchmark .
 FROM debian:jessie
 
+RUN buildDeps='build-essential gcc-multilib g++-multilib git-core curl ca-certificates php5-cli libboost-all-dev'; \
+    set -x \
+    && apt-get update && apt-get install --no-install-recommends -y $buildDeps
+
 COPY . /nativejson-benchmark
 WORKDIR /nativejson-benchmark
 ENV PATH $PATH:/nativejson-benchmark/build
 
-RUN buildDeps='build-essential gcc-multilib g++-multilib git-core curl ca-certificates php5-cli libboost-all-dev'; \
-	set -x \
-	&& apt-get update && apt-get install --no-install-recommends -y $buildDeps \
-	&& cd /nativejson-benchmark \
-	&& git submodule update --init \
-	&& cd build \
+RUN set -x \
+	&& cd /nativejson-benchmark/build \
 	&& curl -L -s https://github.com/premake/premake-core/releases/download/v5.0.0-alpha7/premake-5.0.0-alpha7-linux.tar.gz | tar -xvz \
 	&& chmod +x premake5 && chmod +x premake.sh && sync && /bin/sh -c ./premake.sh && ./machine.sh \
 	&& cd /nativejson-benchmark && make \
 	&& cd /nativejson-benchmark/bin \
 	&& for t in *; do ./$t; done \
-	&& cd /nativejson-benchmark/result && make \
-	&& apt-get purge -y --auto-remove $buildDeps
+	&& cd /nativejson-benchmark/result && make
 
 VOLUME ["/nativejson-benchmark/output"]