Add a lister of all hosted repositories on a Phabricator instance
Closes T808

the exception can also be an AttributeError.

Also do not reraise this exception (in github/tasks.py). This promise
saving feature is used for tests.

Related T1508

Prior to this commit, initializing all listers was failing after the
debian lister processing because of global insert_minimum_data init

Related T1629

Summary:
Using order by and offset makes the partitioning a n^2 operation on the number
of entries in the table, rather than an instant operation when using
min/max.

This assumes the indexable column is more or less uniform, which is not exactly
true but not the worst approximation either.

Test Plan: tox

Reviewers: #reviewers, douardda

Reviewed By: #reviewers, douardda

Subscribers: douardda, swh-public-ci

Differential Revision: https://forge.softwareheritage.org/D1267

Summary:
Using order by and offset makes the partitioning a n^2 operation on the number
of entries in the table, rather than an instant operation when using
min/max.

This assumes the indexable column is more or less uniform, which is not exactly
true but not the worst approximation either.

Test Plan: tox

Reviewers: #reviewers, douardda

Reviewed By: #reviewers, douardda

Subscribers: douardda, swh-public-ci

Differential Revision: https://forge.softwareheritage.org/D1267

making 2 of them fail (in test_bb_lister.py and test_gh_lister.py).

with conventional structure
  { 'cls': cls, 'args': {}}

r

and add a 'all' possibel value for it, so that one can initialize all the
database for all listers at once.

the db query actually returns a table-like (2d) structure.

since this is now handled by the SWHTask itself.

pytest<4 because of https://github.com/pytest-dev/pytest/issues/4641

when this lister is called for the first time, db_num_entries() may return
a null value, so the min() will also be zero, making the range() call crash.

which it won't be when the lister is called for the first time (since
the run() method will be be called with min_bond=None in this case).

so that we can easily manage its configuration (especially in the docker
environment) by referring to this lister as only 'bitbucket' everywhere
(ie. python package name and config file names).

since it's now the default base class in swh-scheduler (>= 0.0.39)