LU-17631 tests: move refresh_krb5_tgt() to test-framework.sh

LU-17631 tests: move refresh_krb5_tgt() to test-framework.sh

refresh_krb5_tgt() is used in multiple test scripts, so move it to
test-framework.sh.

Test-Parameters: trivial kerberos=true testlist=sanity-krb5
Fixes: 478df60923 ("LU-17050 tests: test Kerberos env in sanity-krb5")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I26c5aaf653d332666a08e315425e1befe8cad2b2
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54347
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>