Set uri_v3 in tempest config

This properly sets the v3 uri for keystone in the tempest config.
Previously tempest would just guess the v3 uri by replacing v2 with v3.
However, moving forward this will no longer be the case so devstack
should properly set this uri to enable tempest to use the keystone v3
api in addition to the v2.

Change-Id: Ib02b2e9f24d8ca1f381186c48747ca0fbc45f3f1
diff --git a/lib/tempest b/lib/tempest
index 06183b1..1eea9b6 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -251,6 +251,7 @@
 
     # Identity
     iniset $TEMPEST_CONFIG identity uri "$KEYSTONE_SERVICE_PROTOCOL://$KEYSTONE_SERVICE_HOST:5000/v2.0/"
+    iniset $TEMPEST_CONFIG identity uri_v3 "$KEYSTONE_SERVICE_PROTOCOL://$KEYSTONE_SERVICE_HOST:5000/v3/"
     iniset $TEMPEST_CONFIG identity password "$password"
     iniset $TEMPEST_CONFIG identity alt_username $ALT_USERNAME
     iniset $TEMPEST_CONFIG identity alt_password "$password"