Security and safety improvements for gitlab-workhorse integration

Companion to https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/60

- Use a custom content type when sending data to gitlab-workhorse
- Verify (using JWT and a shared secret on disk) that internal API requests came from gitlab-workhorse

This will allow us to build features in gitlab-workhorse that require
more trust, and protect us against programming mistakes in the future.

This is designed so that no action is required for installations from
source. For omnibus-gitlab we need to add code that manages the shared
secret.

See merge request !5907

Fix intermittent spec failures with spec/features/issues/user_uses_slash_commands_spec.rb

This MR solves the intermittent spec failure:

```
 1) Issues > User uses slash commands behaves like issuable record that supports slash commands in its description and notes note on issue with a note changing the issue's title when current user cannot change title of issue does not reopen the issue
     Failure/Error: Gitlab::Routing.url_helpers.namespace_project_url(self.namespace, self)

     ActionController::UrlGenerationError:
       No route matches {:action=>"show", :controller=>"projects", :id=>#<Project id: 1, name: "project135", path: "gitlabhq", description: nil, created_at: "2016-08-31 20:45:48", updated_at: "2016-08-31 20:45:48", creator_id: 2, issues_enabled: true, merge_requests_enabled: true, wiki_enabled: true, namespace_id: 2, snippets_enabled: true, last_activity_at: "2016-08-31 20:45:48", import_url: nil, visibility_level: 20, archived: false, avatar: nil, import_status: "none", repository_size: 0.0, star_count: 0, import_type: nil, import_source: nil, commit_count: 0, import_error: nil, ci_id: nil, builds_enabled: true, shared_runners_enabled: true, runners_token: "_rNZHgsHzaDWGbyL3L2F", build_coverage_regex: nil, build_allow_git_fetch: true, build_timeout: 3600, pending_delete: false, public_builds: true, pushes_since_gc: 0, last_repository_check_failed: nil, last_repository_check_at: nil, container_registry_enabled: true, only_allow_merge_if_build_succeeds: false, has_external_issue_tracker: false, repository_storage: "default", request_access_enabled: true, has_external_wiki: false, lfs_enabled: nil>, :namespace_id=>nil} missing required keys: [:namespace_id]
     Shared Example Group: "issuable record that supports slash commands in its description and notes" called from ./spec/features/issues/user_uses_slash_commands_spec.rb:6
     # ./app/models/project.rb:611:in `web_url'
     # ./app/models/project.rb:975:in `hook_attrs'
     # ./lib/gitlab/data_builder/note.rb:58:in `build_base_data'
     # ./lib/gitlab/data_builder/note.rb:38:in `build'
     # ./app/services/notes/post_process_service.rb:19:in `hook_data'
     # ./app/services/notes/post_process_service.rb:23:in `execute_note_hooks'
     # ./app/services/notes/post_process_service.rb:14:in `execute'
     # ./app/workers/new_note_worker.rb:10:in `perform'
     # ./app/services/notes/create_service.rb:29:in `execute'
     # ./app/controllers/projects/notes_controller.rb:26:in `create'
     # ./lib/gitlab/request_profiler/middleware.rb:15:in `call'
     # ./lib/gitlab/middleware/go.rb:16:in `call'
     # ./lib/gitlab/middleware/static.rb:9:in `call'
```

There were a number of issues:
    
1. Sidekiq async tasks were being run after project namespaces were deleted. Use Sidekiq in fake mode to prevent this from Sidekiq tasks from being enqueued in the first place.
2. Some outstanding Ajax requests (e.g. autocomplete) were still being loaded while `DatabaseCleaner` ran
3. `logout` did not always wait for logout actually to complete
  
Closes #21723

See merge request !6271

Refresh todos count cache when an Issue/MR is deleted

Fixes #21714

See merge request !6161

* Moves splitting of  `ps` result to helper.
* Users a regexp to extract the different parts

The result of `ps` at least depends on the _LANG_ and the distance of
_start_ to _now_ (start time then the day + hour then month+day)
I've tested with _LANG=en_US.UTF-8_ and _LANG=de_CH.UTF-8_

Closes #20632

See merge request !6245

Sidekiq async tasks were being run after project namespaces were deleted. Use
Sidekiq in fake mode to prevent this from Sidekiq tasks from being enqueued
in the first place.

Closes #21723