Support importing GH projects without rate limits

GitHub Enterprise disables rate limiting for the API, resulting in HTTP
404 errors when requesting rate limiting details. This changes
Gitlab::GithubImport::Client so it can deal with rate limiting being
disabled.

lib/gitlab/github_import/client.rb

@@ -129,6 +129,8 @@ module Gitlab
       # whether we are running in parallel mode or not. For more information see
       # `#rate_or_wait_for_rate_limit`.
       def with_rate_limit
+        return yield unless rate_limiting_enabled?
+
         request_count_counter.increment
 
         raise_or_wait_for_rate_limit unless requests_remaining?
@@ -170,6 +172,10 @@ module Gitlab
         octokit.rate_limit.resets_in + 5
       end
 
+      def rate_limiting_enabled?
+        @rate_limiting_enabled ||= api_endpoint.include?('.github.com')
+      end
+
       def api_endpoint
         custom_api_endpoint || default_api_endpoint
       end

spec/lib/gitlab/github_import/client_spec.rb

@@ -185,6 +185,17 @@ describe Gitlab::GithubImport::Client do
 
       client.with_rate_limit { }
     end
+
+    it 'ignores rate limiting when disabled' do
+      expect(client)
+        .to receive(:rate_limiting_enabled?)
+        .and_return(false)
+
+      expect(client)
+        .not_to receive(:requests_remaining?)
+
+      expect(client.with_rate_limit { 10 }).to eq(10)
+    end
   end
 
   describe '#requests_remaining?' do
@@ -362,4 +373,20 @@ describe Gitlab::GithubImport::Client do
       end
     end
   end
+
+  describe '#rate_limiting_enabled?' do
+    let(:client) { described_class.new('foo') }
+
+    it 'returns true when using GitHub.com' do
+      expect(client.rate_limiting_enabled?).to eq(true)
+    end
+
+    it 'returns false for GitHub enterprise installations' do
+      expect(client)
+        .to receive(:api_endpoint)
+        .and_return('https://github.kittens.com/')
+
+      expect(client.rate_limiting_enabled?).to eq(false)
+    end
+  end
 end