devstack: run tests with tempest run command
devstack: run tests with tempest run command

tempest/tools/pretty_tox_serial.sh is deprecated way and caused test
failure due to version mismatch.
So use tempest run command with tox to run tests.

Change-Id: If896118452e11401723efdab23f044b3e85476ab
Related-bug: #1634940

openstack/networking-odl,openstack/networking-odl,openstack/networking-odl