Fix: DataStore E2E Integration Tests

[ruiguoamz]

Description of changes:
Added a filter inside testCreateMutateDelete(), testCreateThenMutateWithCondition() and testCreateThenMutateWithConditionFailOnSync() to make sure these three tests only care about related payload receiving from hub listener.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[lawmicha]

let post = try? mutationEvent.decodeModel() as? Post above at line 42 will fail the test if there is an existing mutation in the queue and is not a post. if we are enforcing that the hub listener only reacts to data for this test then it should include decoding the right model as well, ie.

guard if let post = try? mutationEvent.decodeModel() as? Post, post.id != newPost.id else {
   return 
}
```

[ruiguoamz]

Something like this?

guard let mutationEvent = payload.data as? MutationEvent else {
      XCTFail("Can't cast payload as mutation event")
      return
}

guard let post = try? mutationEvent.decodeModel() as? Post, post.id != newPost.id else { return }

[palpatim]

I agree with the intent of this proposal, but a couple of things:

1. You need to fix the id equality check:

   guard let post = try? mutationEvent.decodeModel() as? Post, post.id == newPost.id else {
       return
   }

   Otherwise you'll always be guaranteed to check the wrong post.

2. Please add a comment explaining that this check is to protect against stray events being processed after the test has completed, and that it shouldn't be construed as a pattern necessary for production applications.