tests: Add tests for WpSettings object

- settings.c tests conf file loading & parsing, metadata updates,
  wpsetttings object creation and its API.
- settings.lua tests the API from lua scripts.
- Add a sample settings.conf file, this file contains sections copied
  over from client.conf along with the settings section. Add a file
  each for wp side and lua side of scripts.
- Make changes in base test infrastructure to take a custom conf file.
- Enhance the wp_settings_get_instance_api() to be take metadata_name
  parameter. So, Wpsetttings is now a singleton instance for a given
  metadata file.
- Enhance the m-settings module also to be take metadata_name parameter.
  this is handy for lua side of tests as its cumbersome to do this is
  lua.

modules/module-lua-scripting/api/api.c

@@ -1472,11 +1472,17 @@ impl_module_new (lua_State *L)
   }
 }
 
-static int
-get_setting (lua_State *L)
+static gboolean
+get_boolean (lua_State *L)
 {
   const char *setting = luaL_checkstring (L, 1);
-  WpSettings *s = wp_settings_get_instance (get_wp_core (L));
+  const char *metadata_name = NULL;
+
+  if (lua_type (L, 2) == LUA_TSTRING)
+    metadata_name = luaL_checkstring (L, 2);
+
+  WpSettings *s = wp_settings_get_instance (get_wp_core (L), metadata_name);
+
   if (s)
   {
     gboolean value = wp_settings_get_boolean (s, setting);
@@ -1488,7 +1494,7 @@ get_setting (lua_State *L)
 }
 
 static const luaL_Reg settings_methods[] = {
-  { "get_setting", get_setting },
+  { "get_boolean", get_boolean },
   { NULL, NULL }
 };