Comment 0 for bug 2044508

[Impact]

The autopkgtests for Focal are failing due to d/t/mount,
because (un)specified snap revisisions aren't available:

  error: cannot download snap "dragonboard-kernel": no snap revision available as specified

  error: cannot download: no snap revision available as specified: "pc", "pc-kernel"

This isn't a big deal, but might report false-negatives
for autopkgtests regressions for dependencies (example:
SRU for, multipath-tools bug 2039719 comment 12), which
takes some time to check and handle.

The fix is to specify the snap revisions used by model
.assertion files, which fortunately are still the ones
used by the last stable image, in its .manifest files.

[Test Plan]

Check that autopkgtests (specifically, d/t/mount test)
passes for ubuntu-image on Focal.

Expected:

    2185s autopkgtest [08:55:55]: @@@@@@@@@@@@@@@@@@@@ summary
    ...
    2185s mount PASS

Actual:

    4393s autopkgtest [18:40:46]: @@@@@@@@@@@@@@@@@@@@ summary
    ...
    4393s mount FAIL non-zero exit status 1

[Regression Potential]

The changes are limited to `d/t/mount` before running `ubuntu-image`,
and providing downloaded snap files to it, so any regressions would
likely manifest in the test (which is already broken) probably with
snap-related error messages.

[Other Info]

The fix is not required / does not apply to Jammy and later, since
the autopkgtests changed there, and `d/t/mount` is no longer available.

[Error Log]

2690s autopkgtest [18:12:23]: test mount: [-----------------------
2690s ==========> dragonboard-model.assertion
2690s Warning: for backwards compatibility, `ubuntu-image` falls back to `ubuntu-image snap` if no subcommand is given
2690s DEBUG:ubuntu-image:-> [ 0] make_temporary_directories
2690s DEBUG:ubuntu-image:-> [ 1] prepare_gadget_tree
2690s DEBUG:ubuntu-image:-> [ 2] prepare_image
2691s WARNING: proceeding to download snaps ignoring validations, this default will change in the future. For now use --validation=enforce for validations to be taken into account, pass instead --validation=ignore to preserve current behavior going forward
2691s 2023/11/16 18:12:23.373431 store_download.go:142: no host system xdelta3 available to use deltas
2691s error: cannot download snap "dragonboard-kernel": no snap revision available as specified
2691s ERROR:ubuntu-image:COMMAND FAILED: snap prepare-image --channel=stable /tmp/autopkgtest.hdThZq/build.Bhc/src/debian/tests/models/dragonboard-model.assertion /tmp/autopkgtest.hdThZq/autopkgtest_tmp/dragonboard-model/unpack
2691s ERROR:ubuntu-image:Full debug traceback follows
2691s Traceback (most recent call last):
2691s File "/tmp/autopkgtest.hdThZq/build.Bhc/src/ubuntu_image/assertion_builder.py", line 26, in prepare_image
2691s snap(self.args.model_assertion, self.unpackdir,
2691s File "/tmp/autopkgtest.hdThZq/build.Bhc/src/ubuntu_image/helpers.py", line 142, in snap
2691s run(cmd, stdout=None, stderr=None, env=os.environ)
2691s File "/tmp/autopkgtest.hdThZq/build.Bhc/src/ubuntu_image/helpers.py", line 123, in run
2691s proc.check_returncode()
2691s File "/usr/lib/python3.8/subprocess.py", line 448, in check_returncode
2691s raise CalledProcessError(self.returncode, self.args, self.stdout,
2691s subprocess.CalledProcessError: Command '['snap', 'prepare-image', '--channel=stable', '/tmp/autopkgtest.hdThZq/build.Bhc/src/debian/tests/models/dragonboard-model.assertion', '/tmp/autopkgtest.hdThZq/autopkgtest_tmp/dragonboard-model/unpack']' returned non-zero exit status 1.
2691s Traceback (most recent call last):
2691s File "/tmp/autopkgtest.hdThZq/build.Bhc/src/debian/tests/mount", line 50, in <module>
2691s with open(image_file_list, 'r', encoding='utf-8') as fp:
2691s FileNotFoundError: [Errno 2] No such file or directory: '/tmp/autopkgtest.hdThZq/autopkgtest_tmp/dragonboard-model/image-list.txt'
2691s autopkgtest [18:12:24]: test mount: -----------------------]