Enable RSpec/NotToNot cop and auto-correct offenses

Ref: https://gitlab.com/gitlab-org/gitlab-ce/issues/17761

See merge request !4267

Fixed issue with button color when no CI enabled

## What does this MR do?

Fixes an issue with the color of the merge button when no CI is setup.

## What are the relevant issue numbers?

Closes #17844

## Screenshots

![Screen_Shot_2016-05-25_at_09.58.44](/uploads/87aac74c5e2f8bfd2831e99c5915856d/Screen_Shot_2016-05-25_at_09.58.44.png)

See merge request !4287

Signed-off-by: NAlfredo Sumaran <alfredo@gitlab.com>

Fix concurrent request when updating build log in browser

If you have a slow internet connection the trace will not be updated correctly. We need to check if our request is the latest one.

Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/17535

See merge request !4183

Closes #17844

Fix backups if registry is disabled

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17749

See merge request !4263

Changed the Slack build message to use the singular duration if necessary

## What does this MR do?

Previously, the Slack build notification would say "second(s)" even when the duration was only 1 second. This MR fixes that. This is my first time writing Ruby code and my first MR on Gitlab, so feedback is very much appreciated!

See merge request !4253

Update health_check.md - Fix spelling of admin/health_check path.  [ci skip]

## What does this MR do?
Fix the spelling of admin/heath_check to admin/health_check in health_check documentation

## Are there points in the code the reviewer needs to double check?
No

## Why was this MR needed?
Fix a spelling error that may mislead a user on the proper URL/Path to check the GitLab health.

## What are the relevant issue numbers?

## Screenshots (if relevant)

See merge request !4282

Updated snippets UI

![Screen_Shot_2016-05-18_at_14.11.54](/uploads/2544351e50f19a36c4ba9a7a92d5544b/Screen_Shot_2016-05-18_at_14.11.54.png)

Closes #14328

See merge request !4194

Project settings UI update

![Screen_Shot_2016-05-16_at_16.42.55](/uploads/2e308cbf26a002fc411c3e84b663a5d1/Screen_Shot_2016-05-16_at_16.42.55.png)![Screen_Shot_2016-05-16_at_16.43.01](/uploads/8d983c43307c65852efe002f6e9482d9/Screen_Shot_2016-05-16_at_16.43.01.png)![Screen_Shot_2016-05-16_at_16.43.16](/uploads/6124e0600cc0e5b309a60b065409d537/Screen_Shot_2016-05-16_at_16.43.16.png)![Screen_Shot_2016-05-16_at_16.43.13](/uploads/177976c2c08034e096e7ebdcad1f369f/Screen_Shot_2016-05-16_at_16.43.13.png)

See merge request !4162

Clicking changes tab scrolls the window to show the content

When you click on the changes tab in a merge request, it will now scroll the window down to the content.

![scroll](/uploads/c5db23e1c32b1fe62bf4efb815b3f055/scroll.gif)

Closes #15133

See merge request !4192

Also removes the note from the development/testing.md guide

Update branch name from 8-7-stable to 8-8-stable

Fix inconsistency with the command listed above.

[ci skip]

See merge request !4274

Fix typo in link on monitoring help page

Closes #17809

[ci skip]

See merge request !4281

Add CHANGELOG entry about using gitlab-shell v3.0.0



See merge request !4272