refactor zookeeper into a slightly more generic dlm module

This attempts to make the zookeeper installation a bit more modular
(assuming that other folks will want to add other dlms as plugins),
and addresses the service start issues with zookeeper under
ubuntu/upstart.

Zookeeper is not going to be installed by default. Services need to
ask for it with use_dlm.

Change-Id: I33525e2b83a4497a57ec95f62880e0308c88b34f
diff --git a/stackrc b/stackrc
index 76a5756..f4a162b 100644
--- a/stackrc
+++ b/stackrc
@@ -69,7 +69,7 @@
     # Dashboard
     ENABLED_SERVICES+=,horizon
     # Additional services
-    ENABLED_SERVICES+=,rabbit,tempest,mysql,dstat,zookeeper
+    ENABLED_SERVICES+=,rabbit,tempest,mysql,dstat
 fi
 
 # SQLAlchemy supports multiple database drivers for each database server