Rails 5.0 now raises errors when calling rake tasks for test files that don't exist (https://github.com/rails/rails/commit/084a390), which causes a failure when calling rake test:functionals as there is no test/functional/ directory.

This task is used by our jenkins:unit task to run unit/functional tests only, skipping integration tests, so is important.

rake aborted!
LoadError: cannot load such file -- /home/dcleal/code/foreman/foreman/test/functional
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/activesupport-5.0.2.rc1/lib/active_support/dependencies.rb:293:in `require'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/activesupport-5.0.2.rc1/lib/active_support/dependencies.rb:293:in `block in require'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/activesupport-5.0.2.rc1/lib/active_support/dependencies.rb:259:in `load_dependency'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/activesupport-5.0.2.rc1/lib/active_support/dependencies.rb:293:in `require'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/railties-5.0.2.rc1/lib/rails/test_unit/test_requirer.rb:11:in `block in require_files'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/railties-5.0.2.rc1/lib/rails/test_unit/test_requirer.rb:10:in `each'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/railties-5.0.2.rc1/lib/rails/test_unit/test_requirer.rb:10:in `require_files'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/railties-5.0.2.rc1/lib/rails/test_unit/minitest_plugin.rb:62:in `rake_run'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/railties-5.0.2.rc1/lib/rails/test_unit/testing.rake:48:in `block (2 levels) in <top (required)>'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/bin/ruby_executable_hooks:15:in `eval'
/home/dcleal/.rvm/gems/ruby-2.3.0@foreman/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => test:functionals
(See full trace by running task with --trace)

It was removed when I moved test files in #16557, but the empty directory should probably have been kept.