Add some smoke testing to docker image

and correct the entrypoint file to correctly exec and use a shell that exists on
the base alpine image

.docker-entrypoint.sh

@@ -1,6 +1,8 @@
-#!/bin/bash
+#!/bin/sh
 set -e
 
 if [ "${1:0:1}" = '-' ]; then
   set -- travis-worker "$@"
 fi
+
+exec "$@"

.travis.yml

@@ -45,6 +45,7 @@ script:
 - make smoke
 - if [[ $TRAVIS_PULL_REQUEST = 'false' && $QUAY_DOCKER_LOGIN_PASSWORD && $QUAY_DOCKER_LOGIN_USERNAME ]]; then
     make docker-build &&
+    make docker-smoke &&
     make docker-push;
   fi
 - if [[ $TRAVIS_PULL_REQUEST = 'false' && $PACKAGECLOUD_TOKEN ]]; then

utils/docker-smoke

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+set -o errexit
+
+main() {
+  [[ ${DOCKER_DEST} ]] || {
+    __log error="missing \$DOCKER_DEST"
+    exit 1
+  }
+
+  set -o xtrace
+  docker run --rm "${DOCKER_DEST}" --version &>/dev/null
+  docker run --rm "${DOCKER_DEST}" travis-worker --version &>/dev/null
+  docker run --rm "${DOCKER_DEST}" --help &>/dev/null
+  docker run --rm "${DOCKER_DEST}" travis-worker --help &>/dev/null
+}
+
+__log() {
+  echo "time=$(date -u +%Y-%m-%dT%H:%M:%SZ)" "$@"
+}
+
+main "$@"