LU-15626 tests: Fix "error" reported by shellcheck for setup-kerberos

LU-15626 tests: Fix "error" reported by shellcheck for setup-kerberos

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

Change-Id: I803c35b5fc0470a9eeb9ef3c230a0a01adc5b16c
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/46822
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>