fs-util: rewrite chmod_and_chown()

fs-util: rewrite chmod_and_chown()

Inspired by #12431 let's also rework chmod_and_chown() and make sure we
never add more rights to a file not owned by the right user.

Also, let's make chmod_and_chown() just a wrapper arond
fchmod_and_chown().

let's also change strategy: instead of chown()ing first and stating
after on failure and supressing errors, let's avoid the chown in the
firts place, in the interest on keeping things minimal.