Download the box specified by the URL if it doesn't yet exist [closes GH-113]

Thanks a lot to Vitor Pellegrino for much of the work on this.

lib/vagrant/action/vm/check_box.rb

@@ -15,6 +15,8 @@ module Vagrant
             return env.error!(:box_specified_doesnt_exist, :box_name => box_name) if !box_url
 
             env.logger.info "Box #{box_name} not found. Fetching box since URL specified..."
+            Vagrant::Box.add(env.env, box_name, box_url)
+            env.env.load_box!
           end
 
           @app.call(env)

test/test_helper.rb

@@ -32,7 +32,7 @@ class Test::Unit::TestCase
       config.ssh.private_key_path = '~/foo'
 
       config.vm.box = "foo"
-      config.vm.box_url = "http://mycompany.com/protected/my_box.box"
+      config.vm.box_url = nil
       config.vm.box_ovf = "box.ovf"
       config.vm.base_mac = "42"
       config.vm.disk_image_format = 'VMDK'

test/vagrant/action/vm/check_box_test.rb

@@ -32,5 +32,17 @@ class CheckBoxVMActionTest < Test::Unit::TestCase
       assert @env.error?
       assert_equal :box_specified_doesnt_exist, @env.error.first
     end
+
+    should "attempt to download box and continue if URL specified" do
+      seq = sequence("seq")
+      @env.env.config.vm.box_url = "bar"
+      Vagrant::Box.expects(:find).returns(nil)
+      Vagrant::Box.expects(:add).with(@env.env, @env["config"].vm.box, @env["config"].vm.box_url).in_sequence(seq)
+      @env.env.expects(:load_box!).in_sequence(seq)
+      @app.expects(:call).with(@env).once.in_sequence(seq)
+
+      @instance.call(@env)
+      assert !@env.error?
+    end
   end
 end