Update Rake tasks to call `rails test` instead

Also, print out deprecation warning for other rake tasks except
`rake test` and `rake` (default)

Conflicts:
	railties/lib/rails/test_unit/testing.rake
	railties/test/application/rake_test.rb
Merge pull request #10111 from Agis-/patch-1

Remove extra whitespace
removing `rails test`, updating docs to show how to use `rake test`
just use ruby to run tests
add a class for splitting up rake commands
extract test info from the command line and set up the test task
rake test app/model/foo.rb and rake test models/foo works
add integration test for shorthand rake tests
updating the guide
`fast_xs` support has been removed.  Use 'String#encode(xml: :attr)`.
remove unused variables
Merge pull request #10118 from vipulnsward/remove_unused_var_task

remove unused variables
Bring back ActiveRecord::Base#connection_handler removed by mistake on b37399ab
Add option to Class#class_attribute for skipping the query method
Deprecate ActiveRecord#Base.default_scopes?

See #10107.