Use smallint for runner_type since its an enum

db/migrate/20180430101916_add_runner_type_to_ci_runners.rb

@@ -4,6 +4,6 @@ class AddRunnerTypeToCiRunners < ActiveRecord::Migration
   DOWNTIME = false
 
   def change
-    add_column :ci_runners, :runner_type, :integer
+    add_column :ci_runners, :runner_type, :smallint
   end
 end

db/schema.rb

@@ -480,7 +480,7 @@ ActiveRecord::Schema.define(version: 20180503150427) do
     t.integer "access_level", default: 0, null: false
     t.string "ip_address"
     t.integer "maximum_timeout"
-    t.integer "runner_type"
+    t.integer "runner_type", limit: 2
   end
 
   add_index "ci_runners", ["contacted_at"], name: "index_ci_runners_on_contacted_at", using: :btree