New Generic Poller doesn't correctly handle case where Poll request succeeds, but with failed state

[matthchr]

Bug Report

I was specifically testing with github.com/Azure/azure-sdk-for-go/sdk/azcore v1.1.1-0.20220609210213-3e53bd32358a but I think any current version of Poller[T] will have this issue.

This shows up most obviously as a change in behavior of the Poll function of the Poller[T]. In the old, non-generic implementation, a Poll that recieved a valid HTTP response (HTTP status code 200), but whose contents contained a Failed state with an error, would classify that as an error in Golang and return the error to the caller of Poll. You can see this here, the snippet from Poll is:

	if Failed(l.lro.Status()) {
		l.err = shared.NewResponseError(resp)
		l.resp = nil
		return nil, l.err
	}

Now though, if the Poller[T] has a successful response such as:

{"name":"6ec3dd1f-ebf8-4a8c-a8dc-9c5f8fd37358","status":"Failed","startTime":"2022-07-12T20:45:59.39Z","error":{"code":"InternalServerError","message":"An unexpected error occured while processing the request. Tracking ID: 'a675d3d1-a6fd-4938-bafe-e491662d2966'"}}

This is not classified as an error and Poll doesn't return an error. As far as I can tell in the current Poller[T] impl, there is no equivalent "if failed" check. See the code.

[jhendrixMSFT]

Per offline discussion, the pattern is now as follows.

poller := BeginLRO()
for !poller.Done() {
    resp, err := poller.Poll()
    // handle above
}

result, err := poller.Result()
// here's where you discover if the LRO succeeded or failed

[matthchr]

Thanks @jhendrixMSFT!