Add an explicit test-config phase to devstack plugins

This commit adds a new phase to the devstack plugin interface for
configuring test environments. It runs after everything in devstack
(except for the final output commands) to ensure that tempest or
any other dependency is installed prior to running it.

Change-Id: I52128756f18d3857963a0687de77f7cdfd11fb3e

doc/source/plugins.rst

@@ -99,6 +99,8 @@ The current full list of ``mode`` and ``phase`` are:
       should exist at this point.
    -  **extra** - Called near the end after layer 1 and 2 services have
       been started.
+   - **test-config** Called at the end of devstack used to configure tempest
+      or any other test environments
 
 -  **unstack** - Called by ``unstack.sh`` before other services are shut
    down.

stack.sh

@@ -1367,6 +1367,12 @@ if is_service_enabled cinder; then
     fi
 fi
 
+# Run test-config
+# ---------------
+
+# Phase: test-config
+run_phase stack test-config
+
 
 # Fin
 # ===