allow fetcher setup without directory creation

allow fetcher setup without directory creation

apt-get download and changelog as well as apt-helper reuse the acquire
system for their own proposes without requiring the directories the
fetcher wants to create, which is a problem if you run them as non-root
and the directories do not exist as it greets you with:
E: Archives directory /var/cache/apt/archives/partial is missing. -
Acquire (13: Permission denied)

Closes: 762898