LU-15626 tests: Fix "error" reported by shellcheck for sanity-lnet

LU-15626 tests: Fix "error" reported by shellcheck for sanity-lnet

This patch fixes "error" issues reported by shellcheck
for file lustre/tests/sanity-lnet.sh

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I55777e6b65a40c90225c40c29e16fbeb44c3411b
Reviewed-on: https://review.whamcloud.com/46824
Reviewed-by: Aurelien Degremont <degremoa@amazon.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>