This change adds a basic SecureBoot endpoint to the emulator which
returns the actual secure boot enabled status.
The fake and libvirt drivers supports setting the secure boot.
OVMF paths have aligned on /usr/share/OVMF/ since this is supported by
Red Hat and Debian family distros. Default and example firmware loader
is now OVMF_CODE.secboot.fd since this exists on all distros and is
known to work with both secure boot enabled and disabled on some
distros.
Change-Id: Icb85710d81c656da6853d67f5e1c6a8609abc1cf
41628d3546