LU-14724 tests: fix sanityn/77o interop version check

LU-14724 tests: fix sanityn/77o interop version check

Check MDS version is new enough, and not OST version.

Fixes: 345f0d8e56c4 ("LU-14724 nrs: TBF rule list broken when change rule rank")
Test-Parameters: trivial testlist=sanityn serverversion=2.14.0-ddn23
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ibc468d04f92c479920d6e0a424d2603c3b940e72
Reviewed-on: https://review.whamcloud.com/47726
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>