bump(coreos-base/vboot_reference): cgpt bugfix and features!

cgpt next is fixed and will properly failover now.
cgpt create can actually create (or extend) disk image files.
bump(coreos-base/coreos-intaller): minor code update
fix(coreos-base/vboot_reference): Update git hash to merge commit.
Merge pull request #169 from marineam/images

update cgpt and installer