Prevent re-register unless host is in build mode
I'd like to prevent a host from re-registering unless the host is in "build" mode.
Right now, a user who knows a valid activation key can register as a host that already exists and invalidate the subscriptions of the real host. The existing setting `host_profile_assume` can help limit the exposure, but the DMI UUID is not the most well protected piece of host information.
I'd like to request an additional setting to treat an attempt to register as a host that already exists as an error unless that host is in build mode.
From an implementation side, I'd expect this to interact with the `host_profile_assume` setting so that both could be used together.