[git pull] Fixes for Petitboot 1.7.x

[Jeremy Kerr]

Hi Klaus,

> > However, looks like this breaks the CI:
> > 
> >   https://travis-ci.org/open-power/petitboot/builds/628753854
> > 
> > Could you take a look at this?
> 
> I saw that CI break before submitting, but I assumed it was
> something with the CI system, given that the offending
> dm_task_geterrno() function was added by commit 8b9d8bf
> "discover/devmapper: Retry dm-device remove if busy" which is also
> what got tagged with 1.7.4..  I also can't reproduce it locally since
> it apparently builds and "make check" fine on my Ubuntu 18.04.3-
> amd64.
> 
> I'll see if I can repro this on a similar docker build as Travis is 
> using, but any other suggestions are welcome in the meanwhile.

There's a bit of docker infrastructure under the docker/ directory (and
a README) - that should help reproducing, as it should be a very
similar environment to what travis performs.

However, I see that the 1.7.x series failed to build in CI from 1.7.4
onwards:

  https://travis-ci.org/open-power/petitboot/branches

It'd be nice to get this sorted, but maybe not essential? Up to you, if
you're taking on the stable branch :)

Cheers,


Jeremy