Bug#851558: autopkgtest: define Restrictions for tests that aren't suitable for gating CI

[Simon McVittie <smcv@debian.org>]

On Sun, 22 Jan 2017 at 18:07:49 +0000, Simon McVittie wrote:
> Suppose I want to
> test that some tool (ostree or tar or whatever) can back up and restore
> xattrs. I can't test that unless I have some scratch area that lets the
> current user set xattrs.
...
> Or, imagine I want to test a non-http network protocol, perhaps testing
> whether my XMPP client can connect to an XMPP server. As we discussed
> on #851556, we would expect this to work on ci.debian.net, but not on
> Ubuntu's equivalent. I could probe for this with ": | nc xmpp.debian.net 5222"
> or something.
> 
> With Automake, I would be able to exit 77 to get the test recorded as
> having been skipped, but with current autopkgtest I would have to exit 0.
> 
> This would hopefully affect autopkgtest's exit status the same way as if
> the test had been skipped due to "Restrictions: something-you-dont-support" -
> so if one or more tests exit 77, autopkgtest would exit 2.

I've implemented this at
<https://salsa.debian.org/ci-team/autopkgtest/merge_requests/20>
since an implementation is probably easier to comment on than an idea.
It's really orthogonal to what I first asked for in #851558.

    smcv