capistrano multistage without multistage

task :env_1 do
  role :web,          '127.0.0.1'
  role :app,          '127.0.0.1'
  role :db,           '127.0.0.1', :primary => true

  set :rails_env, 'production'
end

task :env_2 do
  role :web,          '127.0.0.1'
  role :app,          '127.0.0.1'
  role :db,           '127.0.0.1', :primary => true

  set :rails_env, 'staging'
end