fix(preflight): improved error reporting for storage container and VM image checks

[thunderboltsid]

• Handle nil responses of get storage container and get cluster API calls.
• Improve error wording.
• Correctly construct error responses of list API calls.
• Test error response of list clusters API call.
• Treat a missing storageContainer as a failed check, but not an internal error.

[dlipovetsky]

Should this handling of the List call be similar to what we have in getVMImages?

cluster-api-runtime-extensions-nutanix/pkg/webhook/preflight/nutanix/image.go

Lines 125 to 137 in 35fd169

	resp, err := client.ListImages(nil, nil, &filter_, nil, nil)
	if err != nil {
	return nil, err
	}
	if resp == nil || resp.GetData() == nil {
	// No images were returned.
	return []vmmv4.Image{}, nil
	}
	images, ok := resp.GetData().([]vmmv4.Image)
	if !ok {
	return nil, fmt.Errorf("failed to get data returned by ListImages")
	}
	return images, nil

[thunderboltsid]

Should this handling of the List call be similar to what we have in getVMImages?

cluster-api-runtime-extensions-nutanix/pkg/webhook/preflight/nutanix/image.go

Lines 125 to 137 in 35fd169

	resp, err := client.ListImages(nil, nil, &filter_, nil, nil)
	if err != nil {
	return nil, err
	}
	if resp == nil || resp.GetData() == nil {
	// No images were returned.
	return []vmmv4.Image{}, nil
	}
	images, ok := resp.GetData().([]vmmv4.Image)
	if !ok {
	return nil, fmt.Errorf("failed to get data returned by ListImages")
	}
	return images, nil

you mean using if conditionals instead of switch conditionals?

[dlipovetsky]

Should this handling of the List call be similar to what we have in getVMImages?

cluster-api-runtime-extensions-nutanix/pkg/webhook/preflight/nutanix/image.go

Lines 125 to 137 in 35fd169

	resp, err := client.ListImages(nil, nil, &filter_, nil, nil)
	if err != nil {
	return nil, err
	}
	if resp == nil || resp.GetData() == nil {
	// No images were returned.
	return []vmmv4.Image{}, nil
	}
	images, ok := resp.GetData().([]vmmv4.Image)
	if !ok {
	return nil, fmt.Errorf("failed to get data returned by ListImages")
	}
	return images, nil

you mean using if conditionals instead of switch conditionals?

Yes, but either is fine.