rely on ErrorCause ToString for the messsage

Author: Mpdreamz

src/Elasticsearch.Net/Responses/Special/BytesResponse.cs

@@ -21,7 +21,7 @@ protected override bool TryGetServerErrorReason(out string reason)
 		{
 			reason = null;
 			if (!this.TryGetServerError(out var serverError)) return false;
-			reason = serverError?.Error?.Reason;
+			reason = serverError?.Error?.ToString();
 			return !reason.IsNullOrEmpty();
 		}
 	}

src/Elasticsearch.Net/Responses/Special/StringResponse.cs

@@ -21,7 +21,7 @@ protected override bool TryGetServerErrorReason(out string reason)
 		{
 			reason = null;
 			if (!this.TryGetServerError(out var serverError)) return false;
-			reason = serverError?.Error?.Reason;
+			reason = serverError?.Error?.ToString();
 			return !reason.IsNullOrEmpty();
 		}
 	}

src/Elasticsearch.Net/Transport/Pipeline/RequestPipeline.cs

@@ -491,7 +491,7 @@ public ElasticsearchClientException CreateClientException<TResponse>(TResponse r
 
 			var exceptionMessage = innerException?.Message ?? $"Request failed to execute";
 			if (response.TryGetServerErrorReason(out var reason))
-				exceptionMessage += $". Error: {reason}";
+				exceptionMessage += $". ServerError: {reason}";
 
 			var pipelineFailure = data.OnFailurePipelineFailure;
 			if (pipelineExceptions.HasAny())

src/Nest/CommonAbstractions/Response/ResponseBase.cs

@@ -57,7 +57,7 @@ public abstract class ResponseBase : IResponse
 
 		bool IElasticsearchResponse.TryGetServerErrorReason(out string reason)
 		{
-			reason = this.ServerError?.Error?.Reason;
+			reason = this.ServerError?.Error?.ToString();
 			return !reason.IsNullOrEmpty();
 		}
 

src/Tests/Reproduce/GithubIssue2985.cs

@@ -34,7 +34,10 @@ public void CanReadSingleOrMultipleCommonGramsCommonWordsItem()
 			);
 			response.OriginalException.Should().NotBeNull().And.BeOfType<ElasticsearchClientException>();
 			response.OriginalException.Message.Should()
-				.Be("Request failed to execute. Error: Custom Analyzer [custom] failed to find filter under name [ascii_folding]");
+				.StartWith("Request failed to execute. ServerError: ")
+				.And.EndWith(
+					"Type: illegal_argument_exception Reason: \"Custom Analyzer [custom] failed to find filter under name [ascii_folding]\""
+				);
 
 			client.DeleteIndex(index);
 		}