gluon-core: add site_config loader script

package/gluon-core/files/usr/lib/lua/gluon/site_config.lua

@@ -0,0 +1,9 @@
+local config = os.getenv('GLUON_SITE_CONFIG') or '/lib/gluon/site.conf'
+
+local function loader()
+   coroutine.yield('return ')
+   coroutine.yield(io.open(config):read('*a'))
+end
+
+-- setfenv doesn't work with Lua 5.2 anymore, but we're using 5.1
+return setfenv(assert(load(coroutine.wrap(loader), 'site.conf')), {})()