Enable the Rubocop DeprecatedClassMethods cop

This reports uses of `File.exists?` and `Dir.exists?`, which were both
deprecated in Ruby and will eventually be removed in favor of
`.exist?`. Also fixes all existing uses of the deprecated methods.

.rubocop.yml

@@ -770,7 +770,7 @@ Lint/DefEndAlignment:
 # Check for deprecated class method calls.
 Lint/DeprecatedClassMethods:
-  Enabled: false
+  Enabled: true
 # Check for duplicate method definitions.
 Lint/DuplicateMethods:

app/models/ci/build.rb

@@ -238,7 +238,7 @@ module Ci
     end
     def recreate_trace_dir
-      unless Dir.exists?(dir_to_trace)
+      unless Dir.exist?(dir_to_trace)
         FileUtils.mkdir_p(dir_to_trace)
       end
     end

app/models/merge_request.rb

@@ -544,7 +544,7 @@ class MergeRequest < ActiveRecord::Base
   end
   def ref_is_fetched?
-    File.exists?(File.join(project.repository.path_to_repo, ref_path))
+    File.exist?(File.join(project.repository.path_to_repo, ref_path))
   end
   def ensure_ref_fetched

config/boot.rb

@@ -3,4 +3,4 @@ require 'rubygems'
 # Set up gems listed in the Gemfile.
 ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
-require 'bundler/setup' if File.exists?(ENV['BUNDLE_GEMFILE'])
+require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])

config/initializers/carrierwave.rb

@@ -2,7 +2,7 @@ CarrierWave::SanitizedFile.sanitize_regexp = /[^[:word:]\.\-\+]/
 aws_file = Rails.root.join('config', 'aws.yml')
-if File.exists?(aws_file)
+if File.exist?(aws_file)
   AWS_CONFIG = YAML.load(File.read(aws_file))[Rails.env]
   CarrierWave.configure do |config|

lib/gitlab/backend/shell.rb

@@ -180,7 +180,7 @@ module Gitlab
     #   exists?('gitlab/cookies.git')
     #
     def exists?(dir_name)
-      File.exists?(full_path(dir_name))
+      File.exist?(full_path(dir_name))
     end
     protected

lib/gitlab/redis.rb

@@ -42,7 +42,7 @@ module Gitlab
       config_file = File.expand_path('../../../config/resque.yml', __FILE__)
   
       @url = "redis://localhost:6379"
-      if File.exists?(config_file)
+      if File.exist?(config_file)
         @url =YAML.load_file(config_file)[rails_env]
       end
     end

spec/config/mail_room_spec.rb

@@ -43,7 +43,7 @@ describe "mail_room.yml" do
       redis_config_file = Rails.root.join('config', 'resque.yml')
       redis_url =
-        if File.exists?(redis_config_file)
+        if File.exist?(redis_config_file)
           YAML.load_file(redis_config_file)[Rails.env]
         else
           "redis://localhost:6379"

spec/services/projects/create_service_spec.rb

@@ -64,7 +64,7 @@ describe Projects::CreateService, services: true do
           @path = ProjectWiki.new(@project, @user).send(:path_to_repo)
         end
-        it { expect(File.exists?(@path)).to be_truthy }
+        it { expect(File.exist?(@path)).to be_truthy }
       end
       context 'wiki_enabled false does not create wiki repository directory' do
@@ -74,7 +74,7 @@ describe Projects::CreateService, services: true do
           @path = ProjectWiki.new(@project, @user).send(:path_to_repo)
         end
-        it { expect(File.exists?(@path)).to be_falsey }
+        it { expect(File.exist?(@path)).to be_falsey }
       end
     end

spec/services/projects/destroy_service_spec.rb

@@ -13,8 +13,8 @@ describe Projects::DestroyService, services: true do
     end
     it { expect(Project.all).not_to include(project) }
-    it { expect(Dir.exists?(path)).to be_falsey }
-    it { expect(Dir.exists?(remove_path)).to be_falsey }
+    it { expect(Dir.exist?(path)).to be_falsey }
+    it { expect(Dir.exist?(remove_path)).to be_falsey }
   end
   context 'Sidekiq fake' do
@@ -24,8 +24,8 @@ describe Projects::DestroyService, services: true do
     end
     it { expect(Project.all).not_to include(project) }
-    it { expect(Dir.exists?(path)).to be_falsey }
-    it { expect(Dir.exists?(remove_path)).to be_truthy }
+    it { expect(Dir.exist?(path)).to be_falsey }
+    it { expect(Dir.exist?(remove_path)).to be_truthy }
   end
   def destroy_project(project, user, params)