Enhancement: add "noautologin" boot parameter

SystemRescue already supports the rootpass and rootcryptpass boot options to specify a root password for the SystemRescue instance. Though the goal of these is clearly to protect against unauthenticated network access, it would be nice to also have some mechanism to disable unauthenticated console access. This is desirable for use cases in which SystemRescue is assigned to a system for network boot to perform an unattended remote operation.