pmb.helpers.git.clone: use git from host system

Preparation for "pmbootstrap pull" (#1858 (closed)).

Let's clean up some legacy cruft first - don't give some repositories ownership to the host system's user and some repositories the ownership of the chroot's pmos user. Instead, give all of them the ownership to the host system's user. Because that is what we did with pmaports.git already, and this way it allows the user to work with the git repository outside of pmbootstrap.

With this simplification, we won't need to pay attention to ownership with the upcoming "pmbootstrap pull" code and it makes the code base more consistent.

Here are four commits, each with a logical change to implement this. See the commit messages for details.