Use the row's own model and host type in regenerate-config

processItems() passed proxyHostModel and the literal "proxy_host" to
configure() for every host type. host_type selects both the template and
the output path, and each host type has its own id sequence, so
redirection hosts, 404 hosts and streams were rendered through
proxy_host.conf and written over /data/nginx/proxy_host/<id>.conf. The
proxy host sharing that id lost its config file and had the resulting
nginx error recorded in its own meta.