[git pull] Fixes for Petitboot 1.7.x

[Jeremy Kerr]

Hi Klaus,

> can you pull the fixes below into 1.7.x? We did some IPL testing on
> a Boston system, and If you're satisfied with them, I think a new
> 1.7.6 release might be tagged.

The changeset looks OK to me, under the assumption that we need to
pull-in new GRUB command support for ongoing compatibility.

However, looks like this breaks the CI:

 https://travis-ci.org/open-power/petitboot/builds/628753854

Could you take a look at this?

For other folks: Klaus and I had a discussion offline, where we
proposed that Klaus would maintain the 1.7.x stable branch, as it's
used in IBM products. Unless there are any objections to that, I'll be
merging patches to 1.7 under his directions.

Cheers,


Jeremy