Add cinder-manage to /usr/local/bin/

This is useful in a dev environment.

Change-Id: I247eb4aea23a906d0e667ec6c5ac79f932bdca24
diff --git a/stack.sh b/stack.sh
index 530fda4..4d649f6 100755
--- a/stack.sh
+++ b/stack.sh
@@ -821,6 +821,7 @@
 
 if [[ "$GLOBAL_VENV" == "True" ]] ; then
     # TODO(frickler): find a better solution for this
+    sudo ln -sf /opt/stack/data/venv/bin/cinder-manage /usr/local/bin
     sudo ln -sf /opt/stack/data/venv/bin/cinder-rtstool /usr/local/bin
     sudo ln -sf /opt/stack/data/venv/bin/glance /usr/local/bin
     sudo ln -sf /opt/stack/data/venv/bin/nova-manage /usr/local/bin