- Move some specs into contexts
- Let get_slugs method take a parameter and return a specific slug.
- Add rescues when using Addressable::URI.

We introduced the feature flag `error_tracking` to test the Sentry MVC
safely.

After the successful test, we remove it again.

Re-use operations controller which already handles tracing settings.

This commit prepares the structure for the upcoming feature error
tracking.

Updates specs to use new rails5 format.

The old format:
`get :show, { some: params }, { some: headers }`

The new format:
`get :show, params: { some: params }, headers: { some: headers }`

This icommit adds several changes related to the same topic
- resetting a Runner registration token:

1. On Project settings page it adds a button for resetting the
   registration token and it removes the Runner token field
   that was confusing all GitLab users.

2. On Group settings page it adds the same button for resetting
   the registration token.

3. On Admin Runners settings page it moves the button to the same
   place as in Project and Group settings and it changes slightly
   the page layout to make it more similar to Group and Project
   setting pages.

4. It refactorizes a little the partial that prints runner
   registration description. Thanks to this Project, Group
   and Admin settings of the Runner are re-using the same
   code to generate the button.

5. Updates the translations of changed text.