refkit-image-common doesn't boot when built with 'ostree' distro feature

[abogani]

On HEAD with these changes in conf/local.conf:

REFKIT_IMAGE_EXTRA_FEATURES += "ostree"
OSTREE_REMOTE = "http://scorfano/ostree/"
OSTREE_EXPORT = "/var/www/ostree"

My Minnowboard dual-E freezes during boot on:
[...]
[ 4.713371] Freeing unused kernel memory: 284K
[ 4.725827] Freeing unused kernel memory: 1036K
starting version 234
root '' doesn't exist or does not contain a /dev.
[...]