chore(*): use COREOS lsb-release variables

update these ebuilds to use the COREOS lsb-release variables

coreos-installer/coreos-installer
cros-devutils/cros-devutils
gmerge/gmerge
update_engine/update_engine
vboot_reference/vboot_reference
Merge pull request #119 from philips/update-everything-to-use-coreos-lsb-release

chore(*): use COREOS lsb-release variables