firewall: Delete and activate zones more efficiently
firewall: Delete and activate zones more efficiently

`update` is deprecated so replacing it with `update2`. This also allows
to only set given properties so we don't need to first read all of them.

martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit