LU-13133 tests: sanity-selinux test_21{a,b} sepol update

LU-13133 tests: sanity-selinux test_21{a,b} sepol update

We need to make sure MDS receives updated sepol info from MGS.
In case of combined MGT/MDT, directly setting fileset on the node
will mask llog-based info retrieval mechanism. So always use
'lctl set_param -P' to set sepol value.

Lustre-change: https://review.whamcloud.com/37224
Lustre-commit: e32ca6e12edbd885838f8a12c0edd455b9ad7105

Test-Parameters: trivial
Test-Parameters: clientselinux testlist=sanity-selinux
Test-Parameters: clientselinux testlist=sanity-selinux
Test-Parameters: clientselinux testlist=sanity-selinux
Test-Parameters: clientselinux testlist=sanity-selinux
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Iaf8ff13364b9ba5f5d8b733be0247d79e05a6b3d
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Etienne AUJAMES <eaujames@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50401
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>