Add debug to tox environment
Add debug to tox environment

The oslotest package distributes a shell file that may be used to assist
in debugging python code. The shell file uses testtools, and supports
debugging with pdb. Debug tox environment implements following test
instructions.
https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests

To enable debugging, run tox with the debug environment. Below are the
following ways to run it.

 * tox -e debug module
 * tox -e debug module.test_class
 * tox -e debug module.test_class.test_method

Change-Id: I08937845803be7bd125b838ab07bda56f202e88d
Closes-Bug: 1632486

jianghuaw/nova,klmitch/nova,Juniper/nova,gooddata/openstack-nova,Juniper/nova,hanlind/nova,rahulunair/nova,jianghuaw/nova,openstack/nova,rajalokan/nova,gooddata/openstack-nova,mahak/nova,rajalokan/nova,mikalstill/nova,hanlind/nova,phenoxim/nova,mikalstill/nova,mikalstill/nova,vmturbo/nova,klmitch/nova,Juniper/nova,mahak/nova,rahulunair/nova,rahulunair/nova,gooddata/openstack-nova,Juniper/nova,jianghuaw/nova,gooddata/openstack-nova,mahak/nova,vmturbo/nova,vmturbo/nova,klmitch/nova,hanlind/nova,openstack/nova,openstack/nova,vmturbo/nova,phenoxim/nova,rajalokan/nova,jianghuaw/nova,klmitch/nova,rajalokan/nova