LU-12751 tests: add missing error()

LU-12751 tests: add missing error()

nothing else I can say

Lustre-change: https://review.whamcloud.com/36159
Lustre-commit: 78f7b7709f9b45b5faae6e7c7b3093c246a08086

Test-Parameters: trivial

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I040771e57ec6f6c6bfbde5a21358c6747f4f20dc
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45578
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alena Nikitenko <anikitenko@ddn.com>