gluon-core: store default domain in UCI

package/gluon-core/luasrc/lib/gluon/upgrade/005-site-domain

+#!/usr/bin/lua
+
+local fs = require 'nixio.fs'
+
+
+if not fs.access('/lib/gluon/domains/') then
+	return
+end
+
+
+local uci = require('simple-uci').cursor()
+
+local domain = uci:get('gluon', 'core', 'domain')
+if domain and not fs.access('/lib/gluon/domains/' .. domain .. '.json') then
+	io.stderr:write(string.format("Warning: invalid mesh domain '%s' configured, resetting to default...\n", domain))
+	domain = nil
+end
+
+if domain then return end
+
+
+-- We can't use gluon.site yet, as it depends on gluon.core.domain to be set
+local json = require 'jsonc'
+local site = assert(json.load('/lib/gluon/site.json'))
+
+uci:set('gluon', 'core', 'domain', site.default_domain)
+uci:commit('gluon')