Fix streaming APIs' Err method closing stream

Fixes calling the Err method on SDK's Amazon Kinesis's SubscribeToShared
and Amazon S3's SelectObjectContent response EventStream members closing
the stream. This would cause unexpected read errors, or early
termination of the streams. Only the Close method of the streaming
members will close the streams.

Improved generated unit and integration tests for streaming API
operations.

Related to aws#2769

private/model/api/eventstream.go

@@ -335,6 +335,8 @@ func (es *{{ $.ShapeName }}) Close() (err error) {
 		es.Writer.Close()
 	{{ end -}}
 
+	es.StreamCloser.Close()
+
 	return es.Err()
 }
 
@@ -353,8 +355,6 @@ func (es *{{ $.ShapeName }}) Err() error {
 		}
 	{{ end -}}
 
-	es.StreamCloser.Close()
-
 	return nil
 }
 
@@ -974,6 +974,16 @@ func (c *loopReader) Read(p []byte) (int, error) {
 			t.Fatalf("expect no error got, %v", err)
 		}
 
+		// Assert calling Err before close does not close the stream.
+		resp.{{ $esMemberName }}.Err()
+		select {
+		case _, ok := <-resp.{{ $esMemberName }}.Events():
+			if !ok {
+				t.Fatalf("expect stream not to be closed, but was")
+			}
+		default:
+		}
+
 		resp.{{ $esMemberName }}.Close()
 		<-resp.{{ $esMemberName }}.Events()