Auto-enable Local HTTP Caching in Test Kitchen, global t-k config

config.yml

<%
require 'socket'

def local_ip
  @local_ip ||= begin
                  # turn off reverse DNS resolution temporarily
                  orig, Socket.do_not_reverse_lookup = Socket.do_not_reverse_lookup, true
                  UDPSocket.open do |s|
      s.connect '64.233.187.99', 1
      s.addr.last
    end
                ensure
                  Socket.do_not_reverse_lookup = orig
                end
end

# http://spin.atomicobject.com/2013/09/30/socket-connection-timeout-ruby/
def socket_open?(host, port, timeout = 0.1)
  addr = Socket.getaddrinfo(host, nil)
  sockaddr = Socket.pack_sockaddr_in(port, addr[0][3])

  Socket.new(Socket.const_get(addr[0][0]), Socket::SOCK_STREAM, 0).tap do |socket|
    socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
    begin
      socket.connect_nonblock(sockaddr)

    rescue IO::WaitWritable
      if IO.select(nil, [socket], nil, timeout)
        begin
          socket.connect_nonblock(sockaddr)
        rescue Errno::EISCONN
          true
        rescue
          socket.close
          false
        end
      else
        socket.close
        false
      end
    end
  end
end

def local_port ; 8123 ; end
def http_proxy_url ; "http://#{local_ip}:#{local_port}" ; end

def proxy_running?
  socket_open?(local_ip, local_port)
end

%>
---
<% if proxy_running? %>
driver:
  http_proxy: <%= http_proxy_url %>
  https_proxy: <%= http_proxy_url %>
provision_command: "env http_proxy=<%= http_proxy_url %> bash -c 'curl -L http://www.opscode.com/chef/install.sh | bash'"
<% end %>