Add keystone middleware to devstack

Add the keystonemiddleware repository to devstack to support testing
with tempest and stable branches.

Change-Id: Ib635465e6568d9cd51d6e432ec8b8633a27d19ce
diff --git a/stack.sh b/stack.sh
index a7f6b2c..5dfe6eb 100755
--- a/stack.sh
+++ b/stack.sh
@@ -722,6 +722,9 @@
     install_heatclient
 fi
 
+# Install middleware
+install_keystonemiddleware
+
 git_clone $OPENSTACKCLIENT_REPO $OPENSTACKCLIENT_DIR $OPENSTACKCLIENT_BRANCH
 setup_develop $OPENSTACKCLIENT_DIR