Merge branch 'show-image-id-on-registry-page' into 'master'

Show proper image ID on registry page

## What does this MR do?
Display the container registry image ID (from the config blob) instead of the first image layer ID

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?
To show proper image ID on container_registry page.
This only supports manifest V2, since the manifest V1 doesn't expose information about Image ID.

## What are the relevant issue numbers?
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18159.

## Screenshots (if relevant)
![Screen_Shot_2016-06-21_at_13.16.44](/uploads/db0d3ed8c8b90fafc8dbf1644c2354b0/Screen_Shot_2016-06-21_at_13.16.44.png)

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4821

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/container_registry/tag.rb b/lib/container_registry/tag.rb
index 7a0929d774e..708d01b95a1 100644
--- a/lib/container_registry/tag.rb
+++ b/lib/container_registry/tag.rb
@@ -3,6 +3,7 @@ module ContainerRegistry
     attr_reader :repository, :name
 
     delegate :registry, :client, to: :repository
+    delegate :revision, :short_revision, to: :config_blob, allow_nil: true
 
     def initialize(repository, name)
       @repository, @name = repository, name