Code review comments applied

app/models/ci/build.rb

@@ -186,7 +186,7 @@ module Ci
       end
 
       after_transition running: any do |build|
-        build.runner_session&.destroy
+        Ci::BuildRunnerSession.where(build: build).delete_all
       end
     end
 

db/migrate/20180613081317_create_ci_builds_runner_session.rb

@@ -8,7 +8,7 @@ class CreateCiBuildsRunnerSession < ActiveRecord::Migration
   DOWNTIME = false
 
   def change
-    create_table :ci_builds_runner_session do |t|
+    create_table :ci_builds_runner_session, id: :bigserial do |t|
       t.integer :build_id, null: false
       t.string :url, null: false
       t.string :certificate

db/schema.rb

@@ -447,7 +447,7 @@ ActiveRecord::Schema.define(version: 20180702114215) do
   add_index "ci_builds_metadata", ["build_id"], name: "index_ci_builds_metadata_on_build_id", unique: true, using: :btree
   add_index "ci_builds_metadata", ["project_id"], name: "index_ci_builds_metadata_on_project_id", using: :btree
 
-  create_table "ci_builds_runner_session", force: :cascade do |t|
+  create_table "ci_builds_runner_session", id: :bigserial, force: :cascade do |t|
     t.integer "build_id", null: false
     t.string "url", null: false
     t.string "certificate"