Devstack provisioning breaks with new demo course

Description

The demo course was updated in https://github.com/openedx/openedx-demo-course/pull/47 and devstack provisioning no longer works. This includes a new course key (new name and org) and the course content being moved a few directories deeper.

We have a temporary workaround to pin the old version of the demo course (https://github.com/openedx-unsupported/devstack/pull/1274) but should put in a more permanent fix. The PR https://github.com/openedx-unsupported/devstack/pull/1272 should fix this as far as the devstack repo itself is concerned, but there seem to be additional references to the course key outside of the devstack repo that might be causing problems.

An attempt to fix this issue

An old PR https://github.com/openedx-unsupported/devstack/pull/1272 can be used as a reference to fix this issue.

首先查看旧的 devstack PR #1272 和临时 workaround PR #1274，然后追踪 devstack 仓库之外对演示课程 key 的引用。完成标准是：devstack provisioning 使用更新后的 openedx-demo-course 即可正常工作，而不再要求旧的固定版本。