first pass at dockerfile support

plugins/config/docker-args-deploy

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$(dirname $0)/../common/functions"
+
+STDIN=$(cat); APP="$1"; IMAGE="dokku/$APP"
+DOCKERFILE_ENV_FILE="$DOKKU_ROOT/$APP/DOCKERFILE_ENV_FILE"
+
+if ! is_image_buildstep_based "$IMAGE"; then
+  > "$DOCKERFILE_ENV_FILE"
+  [[ -f "$DOKKU_ROOT/ENV" ]] && sed -e "s:^export ::g" "$DOKKU_ROOT/ENV" > "$DOCKERFILE_ENV_FILE"
+  [[ -f "$DOKKU_ROOT/$APP/ENV" ]] && sed -e "s:^export ::g" "$DOKKU_ROOT/$APP/ENV" >> "$DOCKERFILE_ENV_FILE"
+
+  echo "$STDIN --env-file=$DOCKERFILE_ENV_FILE"
+else
+  echo "$STDIN"
+fi