LU-15626 tests: Fix "error" reported by shellcheck for sanity-flr.sh

LU-15626 tests: Fix "error" reported by shellcheck for sanity-flr.sh

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

Test-Parameters: trivial testlist=sanity-flr
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I5ce498f9b373650885351ea105121139eb4ed35c
Reviewed-on: https://review.whamcloud.com/46797
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>