Disable Ember CLI Mirage in a specific test

There can be a scenario where you want to disable ember-cli-mirage server in a specific test file; acceptance specially. You can do that by shutting down the Mirage server in `beforeEach()` in an acceptance test. For example,

```
moduleForAcceptance('Acceptance | test name', {
  beforeEach() {
    server.shutdown();
  }
});
```