Bug#648148: autopkgtest: Support running as user

[ijackson@chiark.greenend.org.uk (Ian Jackson)]

tags 648148 - patch
thanks

Hi.  Martin, you wrote:
> for testing build recipes I'd like to skip all the apt parts and run
> adt-run as normal user. This currently fails because it always tries
> to set up apt.

I agree that this would be sensible.  But I think the right answer is
to make this depend on the `root-on-testbed' testbed capability, not
on opts.user.

Also, Jakub, you wrote:
> (Setting TMPDIR was a mistake in the first place IMHO. This variable
> in POSIX has completely different semantics. Running a scripts that
> relied on the feature outside adt-run might lead to security holes.)

I agree.  However I'm not sure that we can just withdraw this.  There
may be tests depending on it, and it's documented in the spec.

I'm tempted to suggest:
 - Invent a new variable ADT_TMP that does what TMPDIR is specified to do.
 - Continue to set TMPDIR, but to a subdirectory of $ADT_TMP but only
   for tests which don't run as root on the testbed.
 - Change the spec to deprecate use of TMPDIR.
 - Change the manpages not to refer to TMPDIR any more.

What do you think ?

Thanks,
Ian.