base dockerfile: add tini, entrypoint that calls /app/entrypoint.sh

[milescrabill]

This PR changes the base dockerfile to use tini as pid 0 for signal handling, and adds a default entrypoint that works for running a10n and bb.

See: https://github.com/mozilla-services/elmo-automation/issues/1

[Pike]

I just tried this locally and got the problem below. Didn't look in much deeper, as I'm on PTO (would have done an easy r+, though)

Fuchsia:elmo-automation axelhecht$ docker-compose build
rabbitmq uses an image, skipping
Building base
Step 1/12 : FROM python:2.7.14-stretch
 ---> eff0ac88f734
Step 2/12 : ENV TINI_VERSION v0.17.0
 ---> Running in e3b319b9794a
Removing intermediate container e3b319b9794a
 ---> 87ab48a49055
Step 3/12 : ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini

 ---> c09b24c76534
Step 4/12 : ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini.asc /tini.asc

 ---> abe813372198
Step 5/12 : RUN gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 595E85A6B1B4779EA4DAAEC70B588DFF0527A9B7  && gpg --verify /tini.asc
 ---> Running in 88d8de339415
gpg: directory '/root/.gnupg' created
gpg: keybox '/root/.gnupg/pubring.kbx' created
gpg: keyserver receive failed: Cannot assign requested address
ERROR: Service 'base' failed to build: The command '/bin/sh -c gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 595E85A6B1B4779EA4DAAEC70B588DFF0527A9B7  && gpg --verify /tini.asc' returned a non-zero code: 2

[milescrabill]

I had that the first time I ran docker-compose build or docker build -t local/elmo_base -f ./base/Dockerfile . - it worked the second time. Not sure what's up with that.

[Pike]

Seems that most people end up referencing tianon/gosu#35 when adding a couple of key servers to try. Could you please add that, too?

[milescrabill]

Good call. Latest push models the base dockerfile off that.

[Pike]

Seems to work more reliably this way, I did get a "unknown cert" thing at one point.