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

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

This patch fixes "error" issues reported by shellcheck
for file lustre/tests/conf-sanity.sh. This patch also
moves spaces to tabs.

Test-Parameters: trivial testlist=conf-sanity
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I381af41adb5267e2fd879d4f8ef2c3ccdc10cdae
Reviewed-on: https://review.whamcloud.com/46823
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>