Fix migration specs that can not run within transaction

db/post_migrate/20170526185921_migrate_build_stage_reference.rb

@@ -3,6 +3,8 @@ class MigrateBuildStageReference < ActiveRecord::Migration
 
   DOWNTIME = false
 
+  disable_ddl_transaction!
+
   def up
     disable_statement_timeout
 

spec/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base_spec.rb

 require 'spec_helper'
 
-describe Gitlab::Database::RenameReservedPathsMigration::V1::RenameBase do
+describe Gitlab::Database::RenameReservedPathsMigration::V1::RenameBase, :truncate do
   let(:migration) { FakeRenameReservedPathMigrationV1.new }
   let(:subject) { described_class.new(['the-path'], migration) }
 

spec/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_projects_spec.rb

 require 'spec_helper'
 
-describe Gitlab::Database::RenameReservedPathsMigration::V1::RenameProjects do
+describe Gitlab::Database::RenameReservedPathsMigration::V1::RenameProjects, :truncate do
   let(:migration) { FakeRenameReservedPathMigrationV1.new }
   let(:subject) { described_class.new(['the-path'], migration) }
 

spec/lib/gitlab/database/rename_reserved_paths_migration/v1_spec.rb

@@ -13,7 +13,7 @@ shared_examples 'renames child namespaces' do |type|
   end
 end
 
-describe Gitlab::Database::RenameReservedPathsMigration::V1 do
+describe Gitlab::Database::RenameReservedPathsMigration::V1, :truncate do
   let(:subject) { FakeRenameReservedPathMigrationV1.new }
 
   before do

spec/migrations/add_head_pipeline_for_each_merge_request_spec.rb

 require 'spec_helper'
 require Rails.root.join('db', 'post_migrate', '20170508170547_add_head_pipeline_for_each_merge_request.rb')
 
-describe AddHeadPipelineForEachMergeRequest do
+describe AddHeadPipelineForEachMergeRequest, :truncate do
   let(:migration) { described_class.new }
 
   let!(:project) { create(:empty_project) }

spec/migrations/migrate_user_activities_to_users_last_activity_on_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 require Rails.root.join('db', 'post_migrate', '20170324160416_migrate_user_activities_to_users_last_activity_on.rb')
 
-describe MigrateUserActivitiesToUsersLastActivityOn, :redis do
+describe MigrateUserActivitiesToUsersLastActivityOn, :redis, :truncate do
   let(:migration) { described_class.new }
   let!(:user_active_1) { create(:user) }
   let!(:user_active_2) { create(:user) }