cli: Fix docker sftp volume mapping

[anomiex]

Changes proposed in this Pull Request:

The previous code was not mapping the volumes correctly. It seemed to be
assuming it was mapping over the target paths rather than the
"src:target" strings.

Also it seems we need to put everything under /home/wordpress, otherwise
the symlinks fail.

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Set up sftp in your docker environment. Then sftp in and see if /var/www/html/wp-content/plugins/jetpack/ has Jetpack.

[github-actions]

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[jeherve]

This works for me. 🚢