gluon-site: add default domain and check for it

This does not do anything yet, as this_domain() is not implemented yet.

Based-on-patch-by: lemoer <git@irrelefant.net>

package/gluon-core/check_site.lua

 need_string(in_site({'site_code'}))
 need_string(in_site({'site_name'}))
+
+-- this_domain() returns nil when multidomain support is disabled
+if this_domain() then
+	function need_domain_name(path)
+		need_string(path)
+		need(path, function(default_domain)
+			local f = io.open(os.getenv('IPKG_INSTROOT') .. '/lib/gluon/domains/' .. default_domain .. '.json')
+			if not f then return false end
+			f:close()
+			return true
+		end, nil, 'be a valid domain name')
+	end
+	need_domain_name(in_site({'default_domain'}))
+end
+
 need_string_match(in_domain({'domain_seed'}), '^' .. ('%x'):rep(64) .. '$')
 
 need_string({'opkg', 'lede'}, false)

scripts/check_site.lua

@@ -18,6 +18,10 @@ function in_domain(var)
 	return var
 end
 
+function this_domain()
+	return nil
+end
+
 
 local function path_to_string(path)
 	return table.concat(path, '/')