Introduce two new guides on UEFI and Secure Boot. In addition, update
the flavors guide to document the secure boot feature (though this doc
should really be removed in near term in favour of the auto-generated
docs, as noted inline).
Note that this change includes our first use of the ':nova:extra-spec:'
cross-reference role and highlights a small bug in that implementation.
This is resolved.
Blueprint: allow-secure-boot-for-qemu-kvm-guests
Change-Id: I4eb370b87ba8d0403c8c0ef038a909313a48d1d6
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>