Currently a system is unconditionally marked broken if any of its "power" commands fail. Except these commands now include configure_netboot, which fetches kernel+initrd images from the distro tree. If that fails (for example because the tree has been removed but beaker_expire_distros hasn't picked up on it yet) the system will be marked broken, even though there's nothing wrong with it.

The difficult part here is that *some* failures from configure_netboot (for example inability to resolve the system's FQDN, or insufficient permissions to write a pxelinux config for it) do indicate an unrecoverable problem which should cause the system to be taken out of service until an administrator can correct them. But some other failures from configure_netboot, like an HTTP error fetching the images, are a problem with the distro tree and do not affect the system itself. We might need some way to distinguish these.