chimney script: add a prompt before deleting the previous blobber

currently, when a user runs chimney script, and if there any previous blobber its data will be erased without warning.

We if there is a previous blobber deployment, we should prompt the user and show a warning telling:
"A blobber already exists on this server. Do you wish to delete blobber currently deployed on this server [N/y]:"

在代码仓库中找到 chimney 脚本，很可能是一个处理 blobber 部署的 shell 脚本。找到它检查现有 blobber 并删除它的部分。使用 'read' 添加一个提示，在删除前请求用户确认。在本地测试脚本，确保警告出现且仅在输入 'y' 或 'Y' 时继续删除。

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