core: Raise predictable error if box metadata downlaod fails

lib/vagrant/box.rb

@@ -103,6 +103,9 @@ module Vagrant
       opts = { headers: ["Accept: application/json"] }
       Util::Downloader.new(url, tf.path, **opts).download!
       BoxMetadata.new(File.open(tf.path, "r"))
+    rescue Errors::DownloaderError => e
+      raise Errors::BoxMetadataDownloadError,
+        message: e.extra_data[:message]
     end
 
     # Checks if the box has an update and returns the metadata, version,

lib/vagrant/errors.rb

@@ -168,6 +168,10 @@ module Vagrant
       error_key(:box_metadata_corrupted)
     end
 
+    class BoxMetadataDownloadError < VagrantError
+      error_key(:box_metadata_download_error)
+    end
+
     class BoxMetadataFileNotFound < VagrantError
       error_key(:box_metadata_file_not_found)
     end

templates/locales/en.yml

@@ -382,6 +382,11 @@ en:
         The metadata associated with the box '%{name}' appears corrupted.
         This is most often caused by a disk issue or system crash. Please
         remove the box, re-add it, and try again.
+      box_metadata_download_error: |-
+        There was an error while downloading the metadata for this box.
+        The error message is shown below:
+
+        %{message}
       box_metadata_file_not_found: |-
         The "metadata.json" file for the box '%{name}' was not found.
         Boxes require this file in order for Vagrant to determine the

test/unit/vagrant/box_test.rb

@@ -219,6 +219,16 @@ describe Vagrant::Box do
       expect(result.name).to eq("foo")
       expect(result.description).to eq("bar")
     end
+
+    it "raises an error if the download failed" do
+      dl = double("downloader")
+      Vagrant::Util::Downloader.stub(new: dl)
+      dl.should_receive(:download!).and_raise(
+        Vagrant::Errors::DownloaderError.new(message: "foo"))
+
+      expect { subject.load_metadata }.
+        to raise_error(Vagrant::Errors::BoxMetadataDownloadError)
+    end
   end
 
   describe "destroying" do