Allow Traefik to run without publishing port

Adds the `publish` option which, if set to false, does not pass `--publish` to
`docker run` when starting Traefik. This is useful when running Traefik
behind a reverse proxy, for example.

test/commands/traefik_test.rb

@@ -25,6 +25,11 @@ class CommandsTraefikTest < ActiveSupport::TestCase
     assert_equal \
       "docker run --name traefik --detach --restart unless-stopped --publish 8080:80 --volume /var/run/docker.sock:/var/run/docker.sock --log-opt max-size=\"10m\" #{@image} --providers.docker --log.level=\"DEBUG\" --accesslog.format=\"json\" --api.insecure --metrics.prometheus.buckets=\"0.1,0.3,1.2,5.0\"",
       new_command.run.join(" ")
+
+    @config[:traefik]["publish"] = false
+    assert_equal \
+      "docker run --name traefik --detach --restart unless-stopped --volume /var/run/docker.sock:/var/run/docker.sock --log-opt max-size=\"10m\" #{@image} --providers.docker --log.level=\"DEBUG\" --accesslog.format=\"json\" --api.insecure --metrics.prometheus.buckets=\"0.1,0.3,1.2,5.0\"",
+      new_command.run.join(" ")
   end
 
   test "run with ports configured" do