uuidgen binary is needed by lib/{neutron,ceph}

When using unstack.sh script on Debian Wheezy, i saw a failing call on
uuidgen binary:

    $ ./unstack.sh
    /home/stack/devstack/lib/neutron: line 83: uuidgen: command not found
    Site keystone disabled.
    [...]

Change-Id: I47e158abce9d090eb839c6e97d9191dc99ccfe55
diff --git a/files/debs/neutron b/files/debs/neutron
index a48a800..fd99677 100644
--- a/files/debs/neutron
+++ b/files/debs/neutron
@@ -24,3 +24,4 @@
 sqlite3
 vlan
 radvd # NOPRIME
+uuid-runtime