xenial: debian/tests/basic-smoke fails to debootstrap stable since the release of buster

[Mauricio Faria de Oliveira]

[Impact]

 * Autopkgtest reports failures/regressions for docker.io on Xenial
   because debian/tests/basic-smoke fails to deboostrap Debian stable,
   since the release of the new stable, Debian buster (July 6th 2019).

 * That caused changes to signatures and debootstrap procedures that
   Xenial packages currently fail to handle.

 * Such failures are false-positives of regressions with regards to
   docker.io code *or* it's dependencies, which are thus flagged as
   causing a regression to a reverse-dependency on autopkgtest.u.c.

 * The solution is to revert to / stick with Debian stretch, which
   has been the stable / status-quo before the buster release, and
   is working correctly on both debian-archive-keyring/debootstrap
   on Xenial.

[Test Case]

 * Run docker.io autopkgtests or just 'debian/tests/basic-smoke'.

[Regression Potential]

 * The 'debootstrap' command on 'debian/tests/basic-smoke' should
   now continue to run past an early error, then hit other issues.

   At this time, it has been verified to finish sucessfully in the
   autopkgtest.ubuntu.com infrastructure, tested against a PPA.

[Other Info]

 * Currently only Xenial is being reported/fixed, although this
   issue might hit Bionic and Focal in the future (with 2+years
   support period, extending over Debian releases) depending on
   whether further changes might be needed post-Buster release.

 * Debian's docker.io package only exists on Buster and later,
   so are not susceptible to this problem right now.

 * Waiting a bit on feedback on Debian bug report / BTS 946313 [1].

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=946313

[Original Description]

With the release of Debian Buster (July 2019) the 'stable' distribution symlink on Debian archives changed from 'stretch' to 'buster'.

This caused issues to 'debootstrap <variant> stable <target> <debian mirror>' on Xenial:
(because of Xenial's older/pre-Buster debian-archive-keyring and debootstrap packages)
1. failure to check signature of the Release file (which can be worked-around with --no-check-gpg)
2. failure to unpack packages (which may need further changes)

Thus just revert back to / stick with Debian Stretch as the suite to debootstrap for tests.

This should prevent it to keep changing to newer releases, which depend on changes/fixes to other packages (not worth it just for the purpose of running 'true' in a docker container.)

Original)

+ debootstrap --variant=minbase stable /tmp/tmp.CmnWmuSeHY http://httpredir.debian.org/debian
I: Retrieving InRelease
I: Checking Release signature
E: Release signed by unknown key (key id DCC9EFBF77E11517)
+ doExit
...
basic-smoke FAIL non-zero exit status 1

With --no-check-gpg)

+ debootstrap --no-check-gpg --variant=minbase stable /tmp/tmp.LbI1tZGEJb http://httpredir.debian.org/debian
I: Retrieving InRelease
I: Retrieving Packages
...
I: Unpacking the base system...
...
W: Failure while installing base packages. This will be re-attempted up to five times.
W: See /tmp/tmp.LbI1tZGEJb/debootstrap/debootstrap.log for details
+ doExit
...
basic-smoke FAIL non-zero exit status 1

With s/stable/stretch/)

+ debootstrap --variant=minbase stretch /tmp/tmp.Eyr81GS2o6 http://httpredir.debian.org/debian
I: Retrieving InRelease
I: Failed to retrieve InRelease
I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
I: Valid Release signature (key id 126C0D24BD8A2942CC7DF8AC7638D0442B90D010)
I: Retrieving Packages
...
I: Base system installed successfully.
+ tar -cC /tmp/tmp.5qp31fXQau .
+ docker import - debian
...
+ docker run --name test debian true
...
++ docker rm -f test
...
++ docker rmi debian
...
+ eval true
++ true
...
basic-smoke PASS
...

[Mauricio Faria de Oliveira (mfo)]

Attached debdiff *NOT* for SRU by itself per [1]
(also version string is intentionally incorrect)

So, for a potential piggyback on the next SRU.
Thus adding tag 'block-proposed-xenial' per [2].

This debdiff will help the next SRU(s) as it will
avoid a false autopkgtest regression on docker.io.

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Staging_low_priority_uploads
[2] https://wiki.ubuntu.com/StableReleaseUpdates#Staging_an_upload

[Mauricio Faria de Oliveira (mfo)]

Testing autopkgtests against a PPA
with this does finish successfully.

Results URL / indices:

- https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-xenial-mfo-lp1855481v2/?format=plain

- - xenial/amd64/d/docker.io/20191206_211222_dc751@/artifacts.tar.gz
- - xenial/amd64/d/docker.io/20191206_211222_dc751@/log.gz
- - xenial/amd64/d/docker.io/20191206_211222_dc751@/result.tar

Results log:

- https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-xenial-mfo-lp1855481v2/xenial/amd64/d/docker.io/20191206_211222_dc751@/log.gz

 ...
 autopkgtest [21:12:10]: @@@@@@@@@@@@@@@@@@@@ summary
 basic-smoke PASS
 docker-in-lxd PASS
 Exit request sent.
 ...

Results exitcode:

    $ curl -sL https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-xenial-mfo-lp1855481v2/xenial/amd64/d/docker.io/20191206_211222_dc751@/result.tar | tar x --to-stdout exitcode
    0