migrate any existing host.cert/key to domain based host.cert/key

we don't remove the old one's yet since existing nginx config
might still be referencing them (not sure)

setup/start.sh

@@ -172,6 +172,9 @@ if ! grep -q "^Restart=" /etc/systemd/system/multi-user.target.wants/nginx.servi
     echo -e "\n[Service]\nRestart=always\n" >> /etc/systemd/system/multi-user.target.wants/nginx.service
     systemctl daemon-reload
 fi
+# remove this migration after 1.10
+[[ -f /etc/nginx/host.cert ]] && cp /etc/nginx/host.cert "/etc/nginx/${arg_admin_domain}.host.cert"
+[[ -f /etc/nginx/host.key ]] && cp /etc/nginx/host.cert "/etc/nginx/${arg_admin_domain}.host.key"
 systemctl start nginx
 
 # bookkeep the version as part of data