GD-Storage: Fix flaky test in StorageModuleTest

* Allow 1 second to write config file to disk during test
* Use ASSERT_TRUE() when the test cannot continue without meeting the
  required condition such as asserting a pointer is not nullptr

Tag: #gd-refactor
Bug: 157533831
Test: atest bluetooth_test_gd
Change-Id: I6740c8b8bdb44097867515007aaa73e9a81c972b