[WIP] Create a more user-friendly Dockerfile for images.#310

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emalloy wants to merge 3 commits intofacebook:mainfrom

emalloy:em/fix_docker_and_make_slim

Commits on Feb 27, 2019

initial simple mcrouter dockerfile, fetch a package and install
emalloy
committed
add entrypoint, if MCROUTER_CONFIG_PATH undefined then use the default one written to /etc/mcrouter/mcrouter.json
emalloy
committed
add MCROUTER_LISTEN_PORT as Dockerfile ENV
emalloy
committed