and by the way, we don't need to monkeypatch xunitparser anymore.
This also reverts commit 59da59e9.

Warning: the reported coverage is much lower than before. But when reading
the previous reports, it seems the coverage was overestimated by large,
mostly because old report did not consider all files in woob dir.

Also for some reason pytest's JUnit XML uses `modules.<name>.<class>`
with the `modules.` prefix so we take it into account in testing grid.

Since py3.4, generating a TestResult out of a TestSuite removes all
TestCases, which prevents from getting info from them.
Since we want info on TestCases, we have to force unittest not to remove
them, by monkeypatching.

xunitparser should be patched but it's unmaintained now.

This commit adds the necessary files to run the CI using Gitlab-CI. For
now, it checks that Weboob builds, then runs the linting script
(checking that every module as an icon and some tests + PyFlakes) and
the unittests. Most of modules unittests cannot run because there is no
backend configured.

Some changes were needed in the pre-existing scripts:
* Edit `weboob_lint` to exit with non-zero code if it finds modules
without icons or tests, so that the build could fail in such a case.
* Edit `run_tests.sh` to set correct exit code on failure and rework
generation of XUNIT output. Also added some doc about useful environment
variables. Added a way to generate an xunit output file when running modules
unittests, passing a `XUNIT_OUT` env variable to `run_tests.sh` script.
* Modification of `setup.cfg` and `run_tests` scripts to handle code
coverage generation. The matching regex in Gitlab for the total code
coverage is `TOTAL: (\d+\%\s*)$)`.

I also added a script to generate a JSON module status matrix from
modules unittests, ready to be sent to a
[Weboob-CI](https://github.com/Phyks/weboob-ci) instance.

NOTE: Required Python modules are taken from the `setup.py` script.
`.ci/requirements.txt` contains the requirements to run the unittests
and the CI, whereas `.ci/requirements_modules.txt` contains the specific
Python modules required at runtime by Weboob modules. The latter could
eventually be replaced by a proper call to `debpydep` script.