docker: fix missing tmp directory

docker/common-setup.sh

@@ -16,6 +16,10 @@ ln -s \
    /code/install.sql \
    /var/www-leftypol/
 
+install -m 775 -o leftypol -g leftypol -d /var/tmp/leftypol
+install -m 775 -o leftypol -g leftypol -d /var/tmp/leftypol/cache
+ln -s /var/tmp/leftypol /var/www-leftypol/tmp
+
 install -m 775 -o leftypol -g leftypol -d /var/www-leftypol/js
 ln -s /code/js/* /var/www-leftypol/js/