This move basically made the tests un-runable on my machine, any "usual" thing fails:

$pytest
$pytest odl
$python -c "import odl; odl.test()"

The only way to fix this for me is by moving the pytest.ini file back into the root folder and creating a conftest.py file that points to the pytest plugins:

# in conftest.py
pytest_plugins = "odl.util.pytest_plugins"

With this, all of the above works perfectly.