Use devstack test-config phase
Use devstack test-config phase

New phase 'test-config' has been introduced by [0].
'test-config' is called at the end of devstack used to configure
tempest or any other test environments.
This patch uses new phase to configure tempest if it is enabled.

Reference:
[0] https://review.openstack.org/#/c/311797/

Change-Id: I8a6a3aeee89c1c08bfa5e630b1cdd8f8a5fa2007

openstack/ironic,NaohiroTamura/ironic,openstack/ironic,NaohiroTamura/ironic,SauloAislan/ironic,SauloAislan/ironic,pshchelo/ironic,pshchelo/ironic