tox.ini: Fix cover by giving the source directory explicitly
tox.ini: Fix cover by giving the source directory explicitly

By default, testr assumes that the name of distribution
([metadata]name in setup.cfg) matches the name of the source directory.
However, they are different for this project.  Fix the problem by
giving the source directory explicitly via an option provided by pbr.

Closes-Bug: #1502002
Change-Id: I7a4f91d6914f187f6486ec6073d559843ef0f550

flavio-fernandes/networking-odl,openstack/networking-odl,FedericoRessi/networking-odl,FedericoRessi/networking-odl,flavio-fernandes/networking-odl,openstack/networking-odl,openstack/networking-odl