package/nginx: use /var/cache/nginx instead of /var/tmp/nginx

package/nginx: use /var/cache/nginx instead of /var/tmp/nginx

move
  http-client-body-temp-path
  http-proxy-temp-path
  http-fastcgi-temp-path
  http-scgi-temp-path
  http-uwsgi-temp-path

from /var/tmp/nginx to /var/cache/nginx

this allows the use of systemd constructs

  LogsDirectory=nginx
  CacheDirectory=nginx

to replace

  ExecStartPre=/usr/bin/mkdir -p /var/log/nginx /var/tmp/nginx

as there isn't a similar construct for /var/tmp.

Signed-off-by: Pascal de Bruijn <p.debruijn@unilogic.nl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>