Related to T2367

due to uninitialized state variables

Currently, a failure happens for some reason. As some internal state variables
are not initialized (they are in fetch_data but not in __init__), this
makes the get_snapshot method fails because of it. Then that's making the
visit update step fails.

Adding the proper initialization for those variables in the __init__ method
should fix it. That will allow the failed state of the visit to be updated
properly in the storage. Associating an empty snapshot to the failed visit.

This should fix issues like [1]

https://sentry.softwareheritage.org/share/issue/ace9143c0f6244b49b18cca49a5aa809/

- blackify all the python files,
- enable black in pre-commit,
- add a black tox environment.

and other arguments in test_converters.py to match model's descriptions.

snapshot_get_latest is deprecated, and one of the call didn't need
to get the branches at all, only the id.

swh-storage >= v0.0.174 requires swh-model objects in other proxies,
so the validation proxy must be before the other ones.

Required by swh-storage >= v0.0.172.

This is already done in the loader.core.

It's the same class with a better name.

That aligns the current behavior with other listers and loaders. That's clearer
when reading task information.

Related to T2134

With this commit, we stop passing parameters to the load method. We pass those
parameters to the loader's constructor.

Towards working on the cli unification

Related to T2134

Allows us to call tests on things other than python3, with the same settings.

Stefano Zacchiroli authored 5 years ago and Antoine R. Dumont committed 5 years ago

Also add missing tests data inclusion instruction.

Related D2082

reusing the same names is (even more) confusing

Will be required by swh-loader-core v0.0.45.

This is (hopefully) a temporary fix that can be removed as soon as
  https://github.com/pypa/pip/issues/6239
is fixed, probably thanks to
  https://github.com/pypa/pip/issues/988

for the sake of consistency.