Use foreman to run application in docker environment

Foreman is installed via a gem rather than bundle install due to the
somewhat contentious instructions on the foreman readme - this also has
the advantage of isolating this from the app.

Dockerfile

@@ -1,5 +1,6 @@
 FROM ruby:2.4.2
 RUN apt-get update -qq && apt-get upgrade -y && apt-get install -y build-essential nodejs && apt-get clean
+RUN gem install foreman
 
 ENV DATABASE_URL mysql2://root:root@mysql/collections_publisher_development
 ENV GOVUK_APP_NAME collections-publisher
@@ -19,4 +20,4 @@ RUN GOVUK_APP_DOMAIN=www.gov.uk RAILS_ENV=production bundle exec rails assets:pr
 
 HEALTHCHECK CMD curl --silent --fail localhost:$PORT || exit 1
 
-CMD bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p $PORT -b '0.0.0.0'"
+CMD foreman run web

Procfile

@@ -1 +1,2 @@
+web: bundle exec unicorn -c ./config/unicorn.rb -p ${PORT:-3078}
 worker: bundle exec sidekiq -C ./config/sidekiq.yml