Subsystem failure doing boot can lock model controller

Subsystem failures during boot can result in the boot thread hanging with the model controller lock held.

I'm filing this as a blocker because this can lock up and entire domain if the server is running in a managed domain. The server will be registered with the domain, and thus will be asked to handle domain updates, but the held model controller lock will result in those updates blocking. This will lock up the domain controller and all slave hosts and servers involved in the operation.