Indicating the location tests directory in oslo_debug_helper
Indicating the location tests directory in oslo_debug_helper

According to [1], we can passing a "-t" argument to
oslo_debug_helper to indicate the directory where tests
are located. This will solves ImportError exception.

[1] https://docs.openstack.org/developer/oslotest/features.html

Change-Id: Ifb290b00e79f9d5236d84163c13571dc74cea4e0
Closes-Bug: #1666560

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib