TRITON-???? Allow changing whether firewalls are enabled by default for new VMs through SAPI setting

[marsell]

Currently, adminui creates all VMs with firewall disabled. Indeed, (IIRC) there are no widgets for enabling a firewall when provisioning though adminui.

In any case, in our use-case we always want the firewall enabled. This patch adds a SAPI setting; when this is enabled, it switches the default. No danger of forgetting then!

Note that this patch does not preclude later adding support for enabling firewalls when provisioning to adminui, since a different default is useful there too.

This has been tested before/after, and is already being used in prod (admittedly only a couple weeks).

[bahamat]

I feel like this would go better in the adminui settings page with the data saved to the adminui moray bucket rather than in sapi.