Move all temporary files directly into /var/tmp

Move all temporary files directly into /var/tmp

When running Pakfire as an unprivileged user, we cannot create temporary
files in a subdirectory which has been created earlier by a different
user.

Hence we now put everything directly into /var/tmp where everyone should
have write permissions all of the time.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>