bump(coreos-base/coreos-init): Enable btrfs resizing on boot.
bump(coreos-base/vboot_reference): New cgpt version

Tolerates btrfs, better protective MBR support and adds hybrid MBR support.
bump(sys-kernel/bootengine): drop resize module

Moving to btrfs means we don't need to resize before mounting.
Merge pull request #403 from marineam/btrfs

btrfs and partitioning updates