machine_batch should batch requests

[tyler-ball]

If a user has a recipe containing the following:

machine_batch "apache cluster" do
  (1..10).each do |i|
    machine "apache_#{i}" do
      machine_options #...
      run_list ["recipe[apache]"]
    end
  end
end

We should be only be making 1 request to AWS to create all 10 machines. With the AWS SDK V2 we can set a min_count and max_count parameter on the create_instances call.

[charlesjohnson]

See also #17, #227

[bpoweski]

This is useful for properly utilizing placement groups.