[PATCH] support: Enhance support_need_proc

[DJ Delorie]

Florian Weimer <fweimer@redhat.com> writes:
> I figured out this much from the comments, but it doesn't make quite
> sense: I don't see anything in our xmkdirp implementation that would
> require this.  And I would assume that directories and files aren't
> different, and that a lack of user mapping would impact creation of
> files in other places, too.

It's the generic "need perms to mkdir".  Checking for /proc and issuing
a meaningful error message is far more useful than xmkdir failing with
"xmkdir: permission denied" with no explaination *why*.

We used to fail all container tests if test-container couldn't mount
/proc but that was changed...