settings: Reduce log verbosity if files can't be opened

Basically reintroducing 2a38b4556e.

src/libstrongswan/settings/settings_parser.y

@@ -255,7 +255,16 @@ bool settings_parser_parse_file(section_t *root, char *name)
 	helper->file_include(helper, name);
 	if (!settings_parser_open_next_file(helper))
 	{
-		DBG1(DBG_CFG, "failed to open config file '%s'", name);
+#ifdef STRONGSWAN_CONF
+		if (streq(name, STRONGSWAN_CONF))
+		{
+			DBG2(DBG_CFG, "failed to open config file '%s'", name);
+		}
+		else
+#endif
+		{
+			DBG1(DBG_CFG, "failed to open config file '%s'", name);
+		}
 	}
 	else
 	{

src/libstrongswan/utils/parser_helper.c

@@ -111,7 +111,7 @@ METHOD(parser_helper_t, file_next, parser_helper_file_t*,
 				array_insert(this->files, ARRAY_TAIL, next);
 				return &next->public;
 			}
-			PARSER_DBG1(&this->public, "unable to open '%s'", name);
+			PARSER_DBG2(&this->public, "unable to open '%s'", name);
 			parser_helper_file_destroy(next);
 		}
 		file->matches->destroy(file->matches);