Dockerfile.buildroot: use dumb-init
Anyone using this image as a pet container for building lots of things
really wants this.
Related:
# CI system will likely use this as a base image.
FROM quay.io/coreos-assembler/coreos-assembler:latest
USER root
-ENTRYPOINT ["/usr/bin/bash"]
+ENTRYPOINT ["/usr/bin/dumb-init", "/usr/bin/bash"]
WORKDIR /root/containerbuild
COPY src src
RUN ./src/install-buildroot.sh && yum clean all && rm src -rf
