Dockerfile for the CI image added (#17).

Dockerfile

@@ -0,0 +1,13 @@
+ARG COMPILER
+
+FROM registry.gitlab.com/offa/docker-images/${COMPILER}:stable
+
+RUN apt-get install -y --no-install-recommends openssl libssl-dev && \
+    mkdir deps && cd deps && \
+    git clone --depth=1 https://github.com/cpputest/cpputest.git cpputest && \
+    cd cpputest && mkdir _build && cd _build && \
+    case ${CXX} in clang* ) export CXXFLAGS="-stdlib=libc++"; esac; \
+    cmake -DC++11=ON -DTESTS=OFF .. && make && make install && \
+    cd ../.. && \
+    cd .. && rm -rf deps
+