Add Docker image for CI building

This docker image is suitable for using for a CI runner to build
vrnetlab images. For example, GitLab CI has a docker runner that can use
this as the image to build with.

Author: plajjan

Diff for: ci-builder-image/Dockerfile

@@ -0,0 +1,10 @@
+FROM debian:stable
+
+RUN apt-get update \
+ && apt-get install -y \
+    curl \
+	docker.io \
+	make \
+ && curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | bash \
+ && apt-get install -y git-lfs \
+ && rm -rf /var/lib/apt/lists/*