Add basic Dockerfile syntax highlighting test files

tests/syntax-tests/highlighted/Dockerfile/Dockerfile

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+ARG architecture=amd64
+FROM $architecture/centos:7
+LABEL com.example.version="0.2.1-beta"
+ARG architecture
+
+ENV INTERESTING_PATH /usr/bin/interesting-software
+
+
+COPY entrypoint.sh /usr/bin/entrypoint.sh
+
+RUN if [ "$architecture" = "i386" ]; then echo "Building i386 docker image" && \
+    linux32 yum update -y && linux32 yum install -y mysql ; \
+    else yum update -y && yum install -y mysql
+
+EXPOSE 80/tcp
+
+VOLUME [/var/lib/mysql/data]
+
+ENTRYPOINT ["/usr/bin/entrypoint.sh"]

tests/syntax-tests/source/Dockerfile/Dockerfile

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+ARG architecture=amd64
+FROM $architecture/centos:7
+LABEL com.example.version="0.2.1-beta"
+ARG architecture
+
+ENV INTERESTING_PATH /usr/bin/interesting-software
+
+
+COPY entrypoint.sh /usr/bin/entrypoint.sh
+
+RUN if [ "$architecture" = "i386" ]; then echo "Building i386 docker image" && \
+    linux32 yum update -y && linux32 yum install -y mysql ; \
+    else yum update -y && yum install -y mysql
+
+EXPOSE 80/tcp
+
+VOLUME [/var/lib/mysql/data]
+
+ENTRYPOINT ["/usr/bin/entrypoint.sh"]