Continue updating environment boxes if metadata not found

Prior to this commit, if a user ran a `vagrant box update` on their
entire environment and one of the boxes did not have a metadata file,
the rest of the boxes in the update would be skipped. This commit fixes
that by ignoring those boxes and showng a warning, so that the rest of
the boxes could check for updates.

plugins/commands/box/command/update.rb

@@ -128,7 +128,13 @@ module VagrantPlugins
             if download_options[:insecure].nil?
               download_options[:insecure] = machine.config.vm.box_download_insecure
             end
-            box_update(box, version, machine.ui, download_options, force)
+
+            begin
+              box_update(box, version, machine.ui, download_options, force)
+            rescue Vagrant::Errors::BoxUpdateNoMetadata => e
+              machine.ui.warn(e)
+              next
+            end
           end
         end
 

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

@@ -405,6 +405,24 @@ describe VagrantPlugins::CommandBox::Command::Update do
             end
           end
 
+          context "ignoring boxes with no metadata" do
+            before do
+              allow(subject).to receive(:with_target_vms) { |&block| block.call machine }
+            end
+
+            let(:box) do
+              box_dir = test_iso_env.box3("foo", "1.0", :virtualbox)
+              box = Vagrant::Box.new(
+                "foo", :virtualbox, "1.0", box_dir, metadata_url: "foo")
+              allow(box).to receive(:has_update?).and_raise(Vagrant::Errors::BoxUpdateNoMetadata, name: "foo")
+              box
+            end
+
+            it "continues to update the rest of the boxes in the environment" do
+              subject.execute
+            end
+          end
+
           context "force flag is specified on the command line" do
             let(:argv) { ["--force"].concat(download_options) }