Restore (and possibly other) operations are not handling errors correctly

[heaths]

A customer reported an issue through CSS about restore operations not always failing correctly. No error HTTP status was reported, but a status monitor still returned an error. According to guidelines, this is expected.

The crux of the issue is here:

azure-sdk-for-net/sdk/keyvault/Azure.Security.KeyVault.Administration/src/RestoreOperationInternal.cs

Lines 218 to 222 in 5f860d9

	if (_value != null && EndTime.HasValue && Error?.Code != null)
	{
	_requestFailedException = new RequestFailedException($"{Error.Message}\nInnerError: {Error.InnerError}\nCode: {Error.Code}");
	throw _requestFailedException;
	}

We likely did not populate Error.Code or maybe not even Error, so we didn't create and/or throw a proper RequestFailedException.

[heaths]

Note that guidelines say we should throw a RequestFailedException: https://azure.github.io/azure-sdk/dotnet_implementation.html#dotnet-lro-return