Lookup latest available installed box if required on update

When performing a box update and the box version has been updated
to be different than the installed version, perform a lookup for
the latest available installed box to allow the update command to
continue successfully

plugins/commands/box/command/update.rb

@@ -100,10 +100,14 @@ module VagrantPlugins
             end
 
             if !machine.box
-              machine.ui.output(I18n.t(
+              collection = Vagrant::BoxCollection.new(@env.boxes_path)
-                "vagrant.errors.box_update_no_box",
+              machine.box = collection.find(machine.config.vm.box, provider || @env.default_provider, "> 0")
-                name: machine.config.vm.box))
+              if !machine.box
-              next
+                machine.ui.output(I18n.t(
+                  "vagrant.errors.box_update_no_box",
+                  name: machine.config.vm.box))
+                next
+              end
             end
 
             name     = machine.box.name

test/unit/plugins/commands/box/command/update_test.rb

@@ -307,6 +307,35 @@ describe VagrantPlugins::CommandBox::Command::Update do
           subject.execute
         end
 
+        context "when box version is updated but previous box exists" do
+
+          let(:collection) { double("collection") }
+
+          it "updates the box" do
+            # First call gets nil result to for lookup
+            expect(machine).to receive(:box).and_return(nil)
+            expect(Vagrant::BoxCollection).to receive(:new).and_return(collection)
+            expect(collection).to receive(:find).and_return(box)
+
+            expect(box).to receive(:has_update?).
+              with(machine.config.vm.box_version,
+              {download_options:
+                {ca_cert: nil, ca_path: nil, client_cert: nil,
+                  insecure: false}}).
+              and_return([md, md.version("1.1"), md.version("1.1").provider("virtualbox")])
+
+            expect(action_runner).to receive(:run).with(any_args) { |action, opts|
+              expect(opts[:box_url]).to eq(box.metadata_url)
+              expect(opts[:box_provider]).to eq("virtualbox")
+              expect(opts[:box_version]).to eq("1.1")
+              expect(opts[:ui]).to equal(machine.ui)
+              true
+            }
+
+            subject.execute
+          end
+        end
+
         context "machine has download options" do
           before do
             machine.config.vm.box_download_ca_cert = "oof"