Merge branch '24386-8-14-rc1-requires-quite-amount-of-downtime' into 'master'

Update 8.14-rc1 migrations to minimize downtime and deploy time

## What does this MR do?

Modify 8.14-rc1 migrations and code to minimize downtime and deploy time

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

No

## Why was this MR needed?

8.14-rc1 migrations took too much time in staging, so we didn't want to take too much downtime in production

## Does this MR meet the acceptance criteria?

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

## What are the relevant issue numbers?


Closes #24386

See merge request !7427

app/models/project.rb

@@ -1334,6 +1334,10 @@ class Project < ActiveRecord::Base
     end
   end
+  def only_allow_merge_if_all_discussions_are_resolved
+    super || false
+  end
+
   private
   def pushes_since_gc_redis_key

db/migrate/20160914131004_only_allow_merge_if_all_discussions_are_resolved.rb

@@ -5,10 +5,7 @@ class OnlyAllowMergeIfAllDiscussionsAreResolved < ActiveRecord::Migration
   disable_ddl_transaction!
   def up
-    add_column_with_default(:projects,
-                            :only_allow_merge_if_all_discussions_are_resolved,
-                            :boolean,
-                            default: false)
+    add_column :projects, :only_allow_merge_if_all_discussions_are_resolved, :boolean
   end
   def down

db/schema.rb

@@ -915,7 +915,7 @@ ActiveRecord::Schema.define(version: 20161109150329) do
     t.boolean "has_external_wiki"
     t.boolean "lfs_enabled"
     t.text "description_html"
-    t.boolean "only_allow_merge_if_all_discussions_are_resolved", default: false, null: false
+    t.boolean "only_allow_merge_if_all_discussions_are_resolved"
   end
   add_index "projects", ["ci_id"], name: "index_projects_on_ci_id", using: :btree

spec/requests/api/projects_spec.rb

@@ -360,6 +360,14 @@ describe API::API, api: true  do
       expect(json_response['only_allow_merge_if_all_discussions_are_resolved']).to be_falsey
     end
+    it 'sets a project as allowing merge if only_allow_merge_if_all_discussions_are_resolved is nil' do
+      project = attributes_for(:project, only_allow_merge_if_all_discussions_are_resolved: nil)
+
+      post api('/projects', user), project
+
+      expect(json_response['only_allow_merge_if_all_discussions_are_resolved']).to be_falsey
+    end
+
     it 'sets a project as allowing merge only if all discussions are resolved' do
       project = attributes_for(:project, { only_allow_merge_if_all_discussions_are_resolved: true })