Add changelog note for running tests with pytest-xdist

Make test database template creation concurrent build_db_cache() is used in tests to create test database templates, i.e. DEFAULT_EMPTY_DB_ID (which is __default_empty_db__) and custom template database using CubicwebTC test_db_id/pre_setup_database API. When running tests in parallel using multiple processes, build_db_cache() may try to build the same database twice. Avoid this by adding synchronisation of process by using a file lock. So when two processes require the same template database, one build the database and others wait it to be created. Use filelock (https://github.com/benediktschmitt/py-filelock) library to have a portable (unix / windows) way for handling locks. Also filelock is packaged in debian: https://packages.debian.org/source/python-filelock

Make test database cache lookup concurrent has_cache() is used to dertermine if the template database already exists or not. When running tests accross multiple process, has_cache() wasn't aware of databases created by other processes because it used a cache to generate the cache... Since the discovering discover_cached_db() time is quite reasonable (it's just about listing file in a directory), let re-generate the cache on cache miss.

Fix flake8 issues since release 3.6.0 Flake8 had a new release which raise new issues, namely: W504: line break after binary operator F841: local variable 'ex' is assigned to but never used W605: invalid escape sequence F821: undefined name 'buffer' (noqa seems the only way to avoid this false positive) Also pin flake8>=3.6 in our tests and make explicit that we use python3 to run flake8 tests.

Stabilize flake8 tests on 3.26 branch Use basepython=python2 or flake8 installed with python3 will raise "[F821] undefined name 'buffer'" Pin flake8 < 3.6 which has new checks that doesn't pass on our current code base.

Fix typo in RDFS URI

[doc] Do not rely on lgc's sphinx_ext This module is broken (getting an ImportError) and I don't want to fix it. The only usage we make of it is for the "autodocstring" directive, and I don't know what it does. Based on the context, replacing autodocstring with either automodule or autoclass and removing sphinx_ext from required Sphinx extensions.

Added tag 3.26.7 for changeset ee4ad63c91e5

[pkg] Version 3.26.7

Fix possible double import of cubes For a new-style cube, if we import "cubicweb_<name>" and then import "cubes.<name>", the cube will be imported twice. cubes.<name> and then cubicweb_name is ok though... When using pyramid, we try to find which cube define a "includeme" by importing them with the name "cubes.<name>", so we (possibly ?) double import all new-style cube. This case may also occur in tests with PyramidCWTest. Touching the import loader to fix this scares me, so let's fix this by testing "cubicweb_<name>" *before* "cubes.name" (for old style cubes, importing cubicweb_<name> raise ImportError).