RUBY-932 Return copy of servers and addresses

Author: estolfo

lib/mongo/cluster.rb

@@ -259,13 +259,17 @@ def addition_allowed?(address)
 
     def servers_list
       @servers_update.synchronize do
-        @servers
+        @servers.reduce([]) do |servers, server|
+          servers << server
+        end
       end
     end
 
     def addresses_list
       @addresses_update.synchronize do
-        @addresses
+        @addresses.reduce([]) do |addresses, address|
+          addresses << address
+        end
       end
     end
   end