Don't use caching anymore, it produces bigger images

And installing the dependencies isn't the biggest problem here: downloading
the dependencies of beat.env.python27 takes way more time and bandwidth anyway

Dockerfile

@@ -36,42 +36,44 @@ ADD $tarball $destdir
 # Install the needed packages
 RUN set -ex \
       && build_deps=' \
-      cmake \
-      dh-autoreconf \
-      gcc \
-      gfortran \
-      libatlas-dev \
-      libc-dev \
-      libfreetype6-dev \
-      libgomp1 \
-      libjpeg-dev \
-      liblapack-dev \
-      libpq-dev \
-      libreadline-dev \
-      make \
-      pkg-config \
-      unzip \
-      wget \
+        cmake \
+        dh-autoreconf \
+        gcc \
+        gfortran \
+        libatlas-dev \
+        libc-dev \
+        libfreetype6-dev \
+        libgomp1 \
+        libjpeg-dev \
+        liblapack-dev \
+        libpq-dev \
+        libreadline-dev \
+        make \
+        pkg-config \
+        unzip \
+        wget \
       ' \
       && apt-get update \
-      && apt-get install -y $build_deps
+      && apt-get install -y $build_deps \
+      && apt-get clean \
 
-# building of the content of the tarball
-RUN make -C $destdir download \
+      # building of the content of the tarball
+      && make -C $destdir download \
       && make -C $destdir \
-      && rm -rf $destdir/pkg $destdir/log
+      && rm -rf $destdir/pkg $destdir/log \
 
-# remove the packages no longer needed, and and some runtime-only ones
-RUN set -ex \
+      # remove the packages no longer needed, and add some runtime-only ones
+      && set -ex \
       && runtime_deps=' \
-      libatlas3-base \
-      libffi6 \
-      libfreetype6 \
-      libjpeg62-turbo \
-      libreadline6 \
+        libatlas3-base \
+        libffi6 \
+        libfreetype6 \
+        libjpeg62-turbo \
+        libreadline6 \
       ' \
       && apt-get purge -y --auto-remove $build_deps \
       && apt-get install -y $runtime_deps \
+      && apt-get clean \
       && rm -rf /var/lib/apt/lists/*
 
 # change the PATH, so we can execute the scripts easily