Add debug testenv in tox
Add debug testenv in tox

Once we add debug testenv, we can use "tox debug -- --debug"
to debug test cases when tox is running.

Change-Id: I8613c96bc1bd696ffa6a55e53441e9dda3e25711

mmasaki/trove,mmasaki/trove,openstack/trove,zhangg/trove,redhat-openstack/trove,mmasaki/trove,openstack/trove,redhat-openstack/trove,hplustree/trove,redhat-openstack/trove,hplustree/trove,zhangg/trove