MAINT: Update zesty to artful for i386 testing

[charris]

The zesty release hit end of life Jan 13, 2018 and it seems that travis
ci tests are failing due to a failure to fetch it. This updates to use
artful. When the bionic LTS comes out in April, we should update again.

[charris]

Just testing to see if this works. If so, I will put it in as the failing tests are annoying.

[eric-wieser]

Fails with

E: Package 'libatlas-dev' has no installation candidate

[charris]

Package 'libatlas-dev' has no installation candidate.

Looks like it has been removed, was previously a dependency of libatlas-base-dev and is gone from there also. I suspect the two have been combined, although it would be nice if ubuntu documented that somewhere. Or maybe there was just a screwup.

The --force-yes option has also been deprecated, but I'm not sure what the replacement should be, there are three possibilities in addition to just removing it altogether. I'll try leaving it out before trying the other options.

[charris]

For future reference:

Force yes; this is a dangerous option that will cause apt to
continue without prompting if it is doing something potentially
harmful. It should not be used except in very special situations.
Using force-yes can potentially destroy your system! Configuration
Item: APT::Get::force-yes. This is deprecated and replaced by
--allow-downgrades, --allow-remove-essential,
--allow-change-held-packages in 1.1.

[charris]

Seems to be fixed now, so squashing.