Update 8.14-rc1 migrations to minimize downtime and deploy time

See https://gitlab.com/gitlab-org/gitlab-ce/issues/24386

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

@@ -912,7 +912,7 @@ 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 })