Added Gitlab::Database.config

This returns the ActiveRecord configuration for the current environment.

While CE doesn't use this very often, EE will use it in a few places for
the database load balancing code. I'm adding this to CE so we don't end
up with merge conflicts in this file.

config/initializers/sidekiq.rb

@@ -42,7 +42,7 @@ Sidekiq.configure_server do |config|
   Gitlab::SidekiqThrottler.execute!
-  config = ActiveRecord::Base.configurations[Rails.env] ||
+  config = Gitlab::Database.config ||
     Rails.application.config.database_configuration[Rails.env]
   config['pool'] = Sidekiq.options[:concurrency]
   ActiveRecord::Base.establish_connection(config)

lib/gitlab/database.rb

@@ -5,8 +5,12 @@ module Gitlab
     # http://dev.mysql.com/doc/refman/5.7/en/integer-types.html
     MAX_INT_VALUE = 2147483647
+    def self.config
+      ActiveRecord::Base.configurations[Rails.env]
+    end
+
     def self.adapter_name
-      ActiveRecord::Base.configurations[Rails.env]['adapter']
+      config['adapter']
     end
     def self.mysql?

spec/lib/gitlab/database_spec.rb

 require 'spec_helper'
-class MigrationTest
-  include Gitlab::Database
-end
-
 describe Gitlab::Database, lib: true do
+  before do
+    stub_const('MigrationTest', Class.new { include Gitlab::Database })
+  end
+
+  describe '.config' do
+    it 'returns a Hash' do
+      expect(described_class.config).to be_an_instance_of(Hash)
+    end
+  end
+
   describe '.adapter_name' do
     it 'returns the name of the adapter' do
       expect(described_class.adapter_name).to be_an_instance_of(String)