Add readable error message when remote data could not be fully imported

lib/gitlab/github_import/importer.rb

@@ -36,7 +36,12 @@ module Gitlab
       end
 
       def handle_errors
-        project.update_column(:import_error, errors.to_json) unless errors.empty?
+        return unless errors.any?
+
+        project.update_column(:import_error, {
+          message: 'The remote data could not be fully imported.',
+          errors: errors
+        }.to_json)
       end
 
       def import_labels

spec/lib/gitlab/github_import/importer_spec.rb

@@ -110,7 +110,9 @@ describe Gitlab::GithubImport::Importer, lib: true do
       end
 
       it 'stores error messages' do
-        errors = [
+        error = {
+          message: 'The remote data could not be fully imported.',
+          errors: [
             { type: :label, url: "https://api.github.com/repos/octocat/Hello-World/labels/bug", errors: "Validation failed: Title has already been taken" },
             { type: :milestone, url: "https://api.github.com/repos/octocat/Hello-World/milestones/1", errors: "Validation failed: Title has already been taken" },
             { type: :issue, url: "https://api.github.com/repos/octocat/Hello-World/issues/1347", errors: "Invalid Repository. Use user/repo format." },
@@ -119,10 +121,11 @@ describe Gitlab::GithubImport::Importer, lib: true do
             { type: :pull_request, url: "https://api.github.com/repos/octocat/Hello-World/pulls/1347", errors: "Validation failed: Validate branches Cannot Create: This merge request already exists: [\"New feature\"]" },
             { type: :wiki, errors: "Gitlab::Shell::Error" }
           ]
+        }
 
         described_class.new(project).execute
 
-        expect(project.import_error).to eq errors.to_json
+        expect(project.import_error).to eq error.to_json
       end
     end
   end