Change replicas to 2 in dev quick start

As the dev quick start will only create two minions, so if when
create 4 replicas, there will be only 2 pods create succeed and
the other 2 pods will be in Pending status.

This patch is updating the replicas to 2 to make sure all pods
in the replication controller can be created successfully.

Change-Id: Ib9373487e76d4296dc412cc8a4f61af1bca94647

doc/source/dev/dev-quickstart.rst

@@ -331,10 +331,10 @@ in the cluster::
 To make it a replicated redis cluster create replication controllers for the redis
 slaves and sentinels::
 
-    sed -i 's/\(replicas: \)1/\1 4/' redis-controller.yaml
+    sed -i 's/\(replicas: \)1/\1 2/' redis-controller.yaml
     magnum rc-create --manifest ./redis-controller.yaml --bay-id $BAY_UUID
 
-    sed -i 's/\(replicas: \)1/\1 4/' redis-sentinel-controller.yaml
+    sed -i 's/\(replicas: \)1/\1 2/' redis-sentinel-controller.yaml
     magnum rc-create --manifest ./redis-sentinel-controller.yaml --bay-id $BAY_UUID
 
 Full lifecycle and introspection operations for each object are supported.  For