Eliminate BootstrapNodes#DIGITAL_OCEAN_1_DEV

Instead of including testing-related bootstrap nodes in the
BootstrapNodes class, this change introduces a Node#withPort method that
allows for obtaining a copy of an existing bootstrap node (e.g.
DIGITAL_OCEAN_1) with a modified port value.

This approach to `with*` methods allows for convenient customization of
value types without sacrificing immutability. See [1] for details.

[1]: http://blog.joda.org/2014/03/valjos-value-java-objects.html

src/main/java/io/bitsquare/network/BootstrapNodes.java

@@ -23,7 +23,6 @@ import java.util.List;
 public interface BootstrapNodes {
 
     Node DIGITAL_OCEAN_1 = Node.at("digitalocean1.bitsquare.io", "188.226.179.109");
-    Node DIGITAL_OCEAN_1_DEV = Node.at("digitalocean1.bitsquare.io", "188.226.179.109", 7367);
 
     /**
      * Alias to the default bootstrap node.

src/main/java/io/bitsquare/network/Node.java

@@ -68,6 +68,13 @@ public final class Node {
         return String.valueOf(port);
     }
 
+    /**
+     * Return a copy of this node with the port updated to the given value.
+     */
+    public Node withPort(int newPort) {
+        return Node.at(this.name, this.ip, newPort);
+    }
+
     @Override
     public boolean equals(Object object) {
         if (this == object)

src/test/java/io/bitsquare/msg/TomP2PTests.java

@@ -89,7 +89,7 @@ public class TomP2PTests {
     // Typically you run the bootstrap node on localhost to test direct connection.
     // If you have a setup where you are not behind a router you can also use a WAN bootstrap node.
     private static final Node BOOTSTRAP_NODE = (FORCED_CONNECTION_TYPE == ConnectionType.DIRECT) ?
-            BootstrapNodes.LOCALHOST : BootstrapNodes.DIGITAL_OCEAN_1_DEV;
+            BootstrapNodes.LOCALHOST : BootstrapNodes.DIGITAL_OCEAN_1.withPort(7367);
 
     private static final PeerAddress BOOTSTRAP_NODE_ADDRESS;