Comment 10 for bug 1536810

It seems to be 'a' that causes the failure.
If i remove 'link_in_boot' then it works.

I've committed a change to maas-iamges to work around this at least temporarily
 http://bazaar.launchpad.net/~maas-images-maintainers/maas-images/maas-ephemerals/revision/268