gnome-ostree: Build a "linux-gnome-ostree" kernel based on the Fedora rawhide config

There's many reasons it's unsustainable to reuse the host kernel, but
the primary two are:

1) For automated server side testing, we need a kernel
2) I want to run RHEL6 as a base system, and that kernel just doesn't
   have features necessary to run the gnome-ostree userspace.  For example,
   it doesn't have the pollable virtual console notification that systemd-login
   needs.