feat: properly label intermediate containers for later cleanup

Dokku 0.18.0 requires new labels for cleanup to work properly, so we need to inject them on all docker commit commands.

Also use DOCKER_BIN environment variable so that it may be swapped out via runtime configuration.

Author: josegonzalez

pre-build-buildpack

@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 set -eo pipefail
 [[ $DOKKU_TRACE ]] && set -x
+export DOCKER_BIN=${DOCKER_BIN:="docker"}
 
 hook-apt-pre-build-buildpack() {
   declare APP="$1"
@@ -56,10 +57,11 @@ sleep 1 # wait so that docker run has not exited before docker attach
 EOF
   )
   CID=$(docker run -d "$IMAGE" /bin/bash -e -c "$COMMAND")
-  #enable logs
-  docker attach "$CID"
-  test "$(docker wait "$CID")" -eq 0
-  docker commit "$CID" "$IMAGE" >/dev/null
+  local DOCKER_COMMIT_LABEL_ARGS=("--change" "LABEL org.label-schema.schema-version=1.0" "--change" "LABEL org.label-schema.vendor=dokku" "--change" "LABEL com.dokku.app-name=$APP" "--change" "LABEL $DOKKU_CONTAINER_LABEL")
+
+  "$DOCKER_BIN" attach "$CID"
+  test "$("$DOCKER_BIN" wait "$CID")" -eq 0
+  "$DOCKER_BIN" commit "${DOCKER_COMMIT_LABEL_ARGS[@]}" "$CID" "$IMAGE" >/dev/null
 }
 
 hook-apt-pre-build-buildpack "$@"