Build docker images with spack inside

This prevents that the executing runner needs to be prepared to access GitHub

Dockerfile

@@ -0,0 +1,19 @@
+# This is a Dockerfile that sets up a simple Docker image for CI testing
+# We need this, because we need to install spack into the Docker image
+# in order to avoid the runners requiring access to Github.
+FROM debian:latest
+MAINTAINER dominic.kempf@iwr.uni-heidelberg.de
+
+RUN export DEBIAN_FRONTEND=noninteractive; \
+  apt-get update && apt-get dist-upgrade --no-install-recommends --yes \
+  && apt-get install --no-install-recommends --yes \
+  build-essential \
+  ca-certificates \
+  git             \
+  procps          \
+  python          \
+  python-dev      \
+  && apt-get clean && rm -rf /var/lib/apt/lists/*
+
+ARG version=master
+RUN git clone -b $version https://github.com/spack/spack.git