admin/heal: Fix deep healing to heal objects under more conditions (#8321)

- Heal if the part.1 is truncated from its original size
- Heal if the part.1 fails while being verified in between
- Heal if the part.1 fails while being at a certain offset

Other cleanups include make sure to flush the HTTP responses
properly from storage-rest-server, avoid using 'defer' to
improve call latency. 'defer' incurs latency avoid them
in our hot-paths such as storage-rest handlers.

Fixes #8319

cmd/xl-v1-utils.go

@@ -174,7 +174,6 @@ func readXLMeta(ctx context.Context, disk StorageAPI, bucket string, object stri
 	if len(xlMetaBuf) == 0 {
 		return xlMetaV1{}, errFileNotFound
 	}
-	logger.GetReqInfo(ctx).AppendTags("disk", disk.String())
 	return xlMetaV1UnmarshalJSON(ctx, xlMetaBuf)
 }