When a node is installed but has no policy, checkin will try to bind it

We treat the 'installed' flag for a node as protecting the node from any attempt to match it to a policy.

If the user ever manages to boot a Microkernel on a node that is marked as 'installed' but has no policy assigned to it (e.g., because the original policy was deleted, or because 'protect_new_nodes' is set to true) the checkin by the MK will cause an attempt to bind the node, with potential data loss.