This is an attempt to fix acsone/setuptools-odoo#10

By installing a .pth file named zzz_odoo_autodiscover.pth that will run last,
but before the main program starts, we can remove the dummy odoo package that
is created by the *nspkg.pth files from setuptools. That leaves a chance to
odoo/__init__.py to run when the main program imports odoo. The declare_namespace
in odoo/addons/__init__.py will then repopulate odoo.addons.__path__.

Yes, that is tricky... it's the price to live on the border line where.
To be spec compliant, odoo/__init__.py should be empty. A better solution is
to be found for v11.

otherwise we are in a situation with a child ns package
without parent, which can confuse python

remove dependency on odoo so odoo-autodiscover
can be installed before odoo

including test for it

Because with tox and ubuntu 16, pip does not get installed in the venv...

Don't attempt to use namespace packages anymore for odoo.addons.
It's definitely impossible as long as there is code in odoo/__init__.py
We simply explore sys.path to find odoo/addons directories and add that
to Odoo's ad_paths.