tree-wide: make slurp mode as local as possible for future-proofing

tree-wide: make slurp mode as local as possible for future-proofing

similar to what PMG/TFAConfig.pm already does.

Otherwise, sub-routine calls would still be affected leading to
unexpected results, like the issue fixed by commit "cluster config:
restrict slurp scope to avoid issue parsing network interfaces".

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>