undo change to Remove use of external folder in package tar (#190)

diff --git a/rules/docker_config.bzl b/rules/docker_config.bzl
index e2e7a45..ca33340 100644
--- a/rules/docker_config.bzl
+++ b/rules/docker_config.bzl
@@ -250,7 +250,7 @@
     remove_repo_cmd = "cd ."
     if ctx.attr.repo_pkg_tar:
         repo_pkg_tar = str(ctx.attr.repo_pkg_tar.label.name)
-        package_name = str(ctx.attr.repo_pkg_tar.label.package)
+        package_name = _EXTERNAL_FOLDER_PREFIX + _WORKSPACE_NAME + "/" + str(ctx.attr.repo_pkg_tar.label.package)
 
         # Expand the tar file pointed by repo_pkg_tar
         expand_repo_cmd = ("mkdir ./%s ; tar -xf %s/%s.tar -C ./%s" %