LU-16125 tests: make sanity-sec more robust with SSK

LU-16125 tests: make sanity-sec more robust with SSK

Encryption related tests in sanity-sec carry out unmount and mount of
clients in order to exercise code with and without the encryption key.
In case SSK is in use, we need to make sure flavors are properly
applied before carrying on.

Lustre-change: https://review.whamcloud.com/48386
Lustre-commit: bee889e87584aa3bd2e6819db73d6adf129460ee

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I92e85dc6dcef43f70a7fe05db94cd18fe66a3a24
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49892
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>