def list_amis(distro)
      amis = Hash.new
      Ubuntu.release(distro).amis.each do |ami|
        amis[build_type(ami.region, ami.arch, ami.root_store, ami.virtualization_type)] = ami.name
      end
      amis
    end
def list_amis(distro)
      amis = Hash.new
      Ubuntu.release(distro).amis.each do |ami|
        amis[build_type(ami.region, ami.arch, ami.root_store, ami.virtualization_type)] = ami.name
      end
      amis
    end
Iterates over the AMIs available for the specified distro.

 === Parameters
 distro<String>:: Release name of the distro to display.

 === Returns
 Hash:: Keys are the AMI type, values are the AMI ID.