Fix bug where projects would appear to be stuck in the forked import state

A race condition existed between when Rails committed the `import_status` to
`started` and when the Sidekiq worker forked a project. If this fork was quick,
it's possible that the worker would attempt to move into the `finished` state
before the `started` state took effect.

As mentioned in https://github.com/mperham/sidekiq/wiki/Problems-and-Troubleshooting#cannot-find-modelname-with-id12345,
we should delay the worker to ensure the DB has a chance to update.

Closes #2736

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.1.0 (unreleased)
+  - Fix bug where projects would appear to be stuck in the forked import state (Stan Hu)
   - Show CI status on all pages where commits list is rendered
   - Automatically enable CI when push .gitlab-ci.yml file to repository
   - Move CI charts to project graphs area

app/models/project.rb

@@ -276,8 +276,10 @@ class Project < ActiveRecord::Base
   end
 
   def add_import_job
+    # Schedule these jobs after 2 seconds to ensure DB changes to import_status
+    # are saved by the time the workers start
     if forked?
-      unless RepositoryForkWorker.perform_async(id, forked_from_project.path_with_namespace, self.namespace.path)
+      unless RepositoryForkWorker.perform_in(2.seconds, id, forked_from_project.path_with_namespace, self.namespace.path)
         import_fail
       end
     else