A few minor Dockerfile enhancements.

[hostmaster]

All these things are cosmetic, but it reduces a docker image size as well

• Dockerfile improvements.

  • fewer RUN
  • COPY --chmod

• Linter warnings are addressed.

  • https://github.com/hadolint/hadolint/wiki/DL3041
  • https://github.com/hadolint/hadolint/wiki/DL3027

[NHAS]

This looks good to me. Thanks!