Merge branch 'gitaly-repo-exists' into 'master'

Make Gitaly RepositoryExists opt-out

See merge request gitlab-org/gitlab-ce!16680

changelogs/unreleased/gitaly-repo-exists.yml

+---
+title: Make Gitaly RepositoryExists opt-out
+merge_request: 16680
+author:
+type: other

lib/gitlab/git/repository.rb

@@ -133,7 +133,7 @@ module Gitlab
       end
 
       def exists?
-        Gitlab::GitalyClient.migrate(:repository_exists) do |enabled|
+        Gitlab::GitalyClient.migrate(:repository_exists, status:  Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |enabled|
           if enabled
             gitaly_repository_client.exists?
           else