base-files: reduce number of `mkdir` calls

base-files: reduce number of `mkdir` calls

The `mkdir` commands supports passing multiple arguments to batch create
multiple folders, instead of calling the tool every single time.

If the creation of one of the folders fails, all other folder are still
created and therefore doesn't change the error handling.

Also stop creating `/etc/` explicitly after subfolders of `/etc/` were
already created.

Signed-off-by: Paul Spooren <mail@aparcar.org>