rails sすると、ActiveRecord::ConnectionNotEstablishedとエラーが出る

###前提

CentOS 6.8
Ruby 2.3.1p112 (2016-04-26 revision 54768)
Rails 4.0.13
Bundler 1.14.6
vagrant 1.9.4
mysql 5.7.18
mysql2 0.4.6
vagrant ssh で接続
dot install教材「Ruby on Rails 4入門」に沿って勉強しています。

rails new myapp -d mysql

でmyappディレクトリを作成。その際にはエラーは何も出なかった。

###実現したいこと
第3回はじめてのRuby on Railsのゴールである、rails sコマンドを実行したときに、Welcome aboard画面が表示される状態

###発生している問題・エラーメッセージ
rails sコマンドを実行すると、

ActiveRecord::ConnectionNotEstablished

Rails.root: /home/vagrant/myapp

というエラーが出てしまう。

Full Traceの結果：

activerecord (4.0.13) lib/active_record/connection_adapters/abstract/connection_pool.rb:546:in `retrieve_connection'
activerecord (4.0.13) lib/active_record/connection_handling.rb:79:in `retrieve_connection'
activerecord (4.0.13) lib/active_record/connection_handling.rb:53:in `connection'
activerecord (4.0.13) lib/active_record/query_cache.rb:51:in `restore_query_cache_settings'
activerecord (4.0.13) lib/active_record/query_cache.rb:43:in `rescue in call'
activerecord (4.0.13) lib/active_record/query_cache.rb:32:in `call'
activerecord (4.0.13) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.13) lib/active_record/migration.rb:373:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.13) lib/active_support/callbacks.rb:373:in `_run__144994080881179548__call__callbacks'
activesupport (4.0.13) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.13) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.13) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.13) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.0.13) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.0.13) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.0.13) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.0.13) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.5) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.13) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
actionpack (4.0.13) lib/action_dispatch/middleware/static.rb:84:in `call'
rack (1.5.5) lib/rack/sendfile.rb:112:in `call'
railties (4.0.13) lib/rails/engine.rb:511:in `call'
railties (4.0.13) lib/rails/application.rb:97:in `call'
rack (1.5.5) lib/rack/lock.rb:17:in `call'
rack (1.5.5) lib/rack/content_length.rb:14:in `call'
rack (1.5.5) lib/rack/handler/webrick.rb:60:in `service'
/usr/local/rbenv/versions/2.3.1/lib/ruby/2.3.0/webrick/httpserver.rb:140:in `service'
/usr/local/rbenv/versions/2.3.1/lib/ruby/2.3.0/webrick/httpserver.rb:96:in `run'
/usr/local/rbenv/versions/2.3.1/lib/ruby/2.3.0/webrick/server.rb:296:in `block in start_thread'

(参考：~/myapp/にてgem listを実行した結果）

*** LOCAL GEMS ***

actionmailer (4.0.13)
actionpack (4.0.13)
activemodel (5.1.1, 4.0.13)
activerecord (5.1.1, 4.0.13)
activerecord-deprecated_finders (1.0.4)
activesupport (5.1.1, 4.0.13)
arel (8.0.0, 4.0.2)
bigdecimal (default: 1.2.8)
builder (3.1.4)
bundler (1.14.6)
coffee-rails (4.0.1)
coffee-script (2.4.1)
coffee-script-source (1.12.2)
concurrent-ruby (1.0.5)
did_you_mean (1.0.0)
erubis (2.7.0)
execjs (2.7.0)
hike (1.2.3)
i18n (0.8.1)
io-console (default: 0.4.5)
jbuilder (1.5.3)
jquery-rails (3.1.4)
json (1.8.6, default: 1.8.3)
libv8 (3.16.14.19 x86_64-linux)
mail (2.6.5)
mime-types (3.1)
mime-types-data (3.2016.0521)
minitest (5.8.3, 4.7.5)
multi_json (1.12.1)
mysql2 (0.4.6)
net-telnet (0.1.1)
power_assert (0.2.6)
psych (default: 2.0.17)
rack (1.5.5)
rack-test (0.6.3)
rails (4.0.13)
railties (4.0.13)
rake (12.0.0, 10.4.2)
rdoc (4.3.0, default: 4.2.1)
ref (2.0.0)
rubygems-update (2.6.12)
sass (3.2.19)
sass-rails (4.0.5)
sdoc (0.4.2)
sprockets (3.7.1, 2.12.4)
sprockets-rails (2.3.3)
test-unit (3.1.5)
therubyracer (0.12.3)
thor (0.19.4)
thread_safe (0.3.6)
tilt (1.4.1)
turbolinks (5.0.1)
turbolinks-source (5.0.3)
tzinfo (1.2.3, 0.3.53)
uglifier (3.2.0)

###該当のソースコード
myapp以下
https://github.com/ttykwb1017/dot-instrall-rails

抜粋

Gemfile

ource 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.13'

# Use mysql as the database for Active Record
gem 'mysql2'

# Use SCSS for stylesheets
gem 'sass-rails', '~> 4.0.2'

# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'

# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '~> 4.0.0'

# See https://github.com/sstephenson/execjs#readme for more supported runtimes
 gem 'therubyracer', platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails'

# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'

# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 1.2'

group :doc do
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc', require: false
end

# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use unicorn as the app server
# gem 'unicorn'

# Use Capistrano for deployment
# gem 'capistrano', group: :development

# Use debugger
# gem 'debugger', group: [:development, :test]

###試したこと
ググっても該当する情報があまりなく、何もしていない

どう対処すべきでしょうか。
ご教授頂けると幸いです。