LU-12314 tests: Add Missing Description to sanity test 258a

LU-12314 tests: Add Missing Description to sanity test 258a

This patch adds missing test description to sanity test 258a.

This patch is a back port from master:
Lustre-change: https://review.whamcloud.com/34902
Lustre-commit: ef2a05a61b4201af612356f78197a57b427260b2

Test-Parameters: trivial

Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I972549cd049b965c9e6da9b43aa245bab875a77a
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-on: https://review.whamcloud.com/35245
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>