Configure devstack gate to use UUID tokens

Using uuid tokens will result in faster test runs as there wouldn't
be a need for time.sleep in the rbac_utils.py.

For environments that use fernet tokens, continue to use the
time.sleep(1).

Change-Id: I82eda2e23bee412c3b7bb375649cae43b6f6c061
diff --git a/contrib/post_test_hook.sh b/contrib/post_test_hook.sh
index b864a9b..34555fb 100644
--- a/contrib/post_test_hook.sh
+++ b/contrib/post_test_hook.sh
@@ -35,6 +35,11 @@
 # Import devstack function 'iniset'.
 source $BASE/new/devstack/functions
 
+# Use uuid tokens for faster test runs
+KEYSTONE_CONF=/etc/keystone/keystone.conf
+iniset $KEYSTONE_CONF token provider uuid
+sudo service apache2 restart
+
 # First argument is expected to contain value equal either to 'admin' or
 # 'member' (both lower-case).
 RBAC_ROLE=$1