Mark the import as failed if a temporary or unknown error happened.

I've seen some users have reported that the updated of their mirror
repositories is being stuck, it basically happens because a temporary or
unknown error happened and the import status was kept in `started`
instead of being marked as `failed`.

app/workers/repository_update_mirror_worker.rb

 class RepositoryUpdateMirrorWorker
+  class UpdateMirrorError < StandardError; end
+
   include Sidekiq::Worker
   include Gitlab::ShellAdapter
 
   LEASE_TIMEOUT = 300
-  
+
   sidekiq_options queue: :gitlab_shell
 
   attr_accessor :project, :repository, :current_user
 
   def perform(project_id)
-    return unless try_obtain_lease(project_id)
+    begin
+      return unless try_obtain_lease(project_id)
 
-    @project = Project.find(project_id)
-    @current_user = @project.mirror_user || @project.creator
+      @project = Project.find(project_id)
+      @current_user = @project.mirror_user || @project.creator
 
-    result = Projects::UpdateMirrorService.new(@project, @current_user).execute
-    if result[:status] == :error
-      project.mark_import_as_failed(result[:message])
-      return
-    end
+      result = Projects::UpdateMirrorService.new(@project, @current_user).execute
+      if result[:status] == :error
+        project.mark_import_as_failed(result[:message])
+        return
+      end
 
-    project.import_finish
+      project.import_finish
+    rescue => ex
+      project.mark_import_as_failed("We're sorry, a temporary error happened, please try again.")
+
+      raise UpdateMirrorError, "#{ex.class}: #{ex.message}"
+    end
   end
 
   private

app/workers/repository_update_remote_mirror_worker.rb

 class RepositoryUpdateRemoteMirrorWorker
+  class UpdateRemoteMirrorError < StandardError; end
+
   include Sidekiq::Worker
   include Gitlab::ShellAdapter
 
   sidekiq_options queue: :gitlab_shell
 
   def perform(remote_mirror_id)
-    remote_mirror = RemoteMirror.find(remote_mirror_id)
-    project       = remote_mirror.project
-    current_user  = project.creator
-    result        = Projects::UpdateRemoteMirrorService.new(project, current_user).execute(remote_mirror)
+    begin
+      remote_mirror = RemoteMirror.find(remote_mirror_id)
+      project       = remote_mirror.project
+      current_user  = project.creator
+      result        = Projects::UpdateRemoteMirrorService.new(project, current_user).execute(remote_mirror)
+
+      if result[:status] == :error
+        remote_mirror.mark_as_failed(result[:message])
+      else
+        remote_mirror.update_finish
+      end
+    rescue => ex
+      remote_mirror.mark_as_failed("We're sorry, a temporary error happened, please try again.")
 
-    if result[:status] == :error
-      remote_mirror.mark_as_failed(result[:message])
-    else
-      remote_mirror.update_finish
+      raise UpdateRemoteMirrorError, "#{ex.class}: #{ex.message}"
     end
   end
 end