Fixes issues in cpolicy where merge would modify caller

In cpolicy, when Merge is called it modifies the callers rules which is
not the desired behavior. This adds the creation of a new node that is
used to contain the merged rules.

control/plugin/cpolicy/node.go

@@ -224,11 +224,17 @@ func (c ConfigPolicyNode) Merge(n ctree.Node) ctree.Node {
 	cd := n.(*ConfigPolicyNode)
 	// For the rules in the passed ConfigPolicyNode(converted) add each rule to
 	// this ConfigPolicyNode overwriting where needed.
+	no := NewPolicyNode()
+	for _, r := range c.rules {
+		no.Add(r)
+	}
+
 	for _, r := range cd.rules {
-		c.Add(r)
+
+		no.Add(r)
 	}
 	// Return modified version of ConfigPolicyNode(as ctree.Node)
-	return c
+	return no
 }
 
 // addRulesToConfigPolicyNode accepts a map of empty interfaces that will be