GOPROXY is used to download packages from fastest source,
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This fixes 92130619 formatting.

erp5.recipe.w3validator is not installed, it was just a version pin
because when running buildout updating the software needs a version
pin, by now all softwares must have been updated.

These tests are still using `python setup.py test` which installs
missing packages to their latest versions. Recently, certifi (a
requests dependency) published a new release with python3 only
syntax, so running the test now got an error installing missing
packages:

    File "parts/slapos-package/playbook/roles/standalone-shared/.eggs/certifi-2022.5.18.1-py2.7.egg/certifi/core.py", line 17
        def where() -> str:
                    ^
    SyntaxError: invalid syntax

The `playbook/roles/standalone-shared` is defined on the test suite
as instance parameters, so it seems we can not already install this
package directly from playbook/roles/standalone-shared because
test suite may define something different. For now, just install
requests. All this will have to be addressed when we change this
test to pre-install packages with slapos and use `python -m unittest`
instead of `python setup.py test`.

These two options were unusable for software releases using python3.

This also adds test coverage for the recipe.

These are not supposed to be executed directly

See merge request nexedi/slapos!1179

This reverts commit 4fa33dfc.

This patch is not complete, backporting full support of
`__{code,defaults}__` on Zope2 would require patching more, so we
decided to keep using func_code with ERP5 on Zope2 and to use
__code__ only with ERP5 on Zope4

Extend the upgrade tests to create data before the upgrade, to
confirm that this data can still be found after the upgrade.

This also extends the test to confirm that after upgrade, inituser
can still login, create content and find content created before and
after upgrade.

After 4fa33dfc (erp5: py3: `func_{code,defaults}` was replaced in
Python3 by `__{code,defaults}__`., 2022-04-25), this was no longer
the case, because during indexation, using existing scripts failed
with AttributeError __code__

There is no real control over port chosen by push/pull.

There is no reason to keep python2 compatibility, as python3 flavour of the
KVM software release is good enough.

Thanks to recent increased test coverage python3 compatibility issue was
spotted, and can be fixed.

That's nothing wrong with such small disk, and the default seems reasonable
enough.

external-disk-* parameters are fully tested, including it's special features
like keeping the image available even in case of dropping them from request
parameters.