RouterErrorCode processServerError(ServerErrorCode errorCode) {
      return RouterErrorCode.UnexpectedInternalError;
    }
Process the given {@link ServerErrorCode} and set operation status accordingly.
Receiving a {@link ServerErrorCode#BlobDeleted}, {@link ServerErrorCode#BlobExpired} or
{@link ServerErrorCode#BlobNotFound} is unexpected for all chunks except for the first.
@param errorCode the {@link ServerErrorCode} to process.
@return the {@link RouterErrorCode} mapped from input server error code.
ambry-router/src/main/java/com/github/ambry/router/GetBlobOperation.java