Add index name to ICreateIndexResponse (#3827)

* Add index name to ICreateIndexResponse

Fixes #3823

* Index is returned in Elasticsearch 6.0.0, so condition is not needed

Author: codebrain

src/Nest/Indices/IndexManagement/CreateIndex/CreateIndexResponse.cs

@@ -7,10 +7,15 @@ public interface ICreateIndexResponse : IAcknowledgedResponse
 	{
 		[JsonProperty("shards_acknowledged")]
 		bool ShardsAcknowledged { get; }
+
+		[JsonProperty("index")]
+		string Index { get; }
 	}
 
 	public class CreateIndexResponse : AcknowledgedResponseBase, ICreateIndexResponse
 	{
 		public bool ShardsAcknowledged { get; set; }
+
+		public string Index { get; set; }
 	}
 }

src/Tests/Tests/Indices/IndexManagement/CreateIndex/CreateIndexApiTests.cs

@@ -205,6 +205,7 @@ protected override void ExpectResponse(ICreateIndexResponse response)
 			response.ShouldBeValid();
 			response.Acknowledged.Should().BeTrue();
 			response.ShardsAcknowledged.Should().BeTrue();
+			response.Index.Should().Be(CallIsolatedValue);
 
 			var indexSettings = Client.GetIndexSettings(g => g.Index(CallIsolatedValue));