Merge pull request #6 from racker/dev/songgao

merge: agent now talks to endpoint through stud! (no successful handshake yet)
Fixed a bug that vm_ok.sh does not detect 'aborted' status
using pingpong for better testing output
Merge pull request #11 from racker/songgao/using_pingpong_for_testing_output

using pingpong for better testing output
Merge pull request #10 from racker/songgao/fix_vm_ok_not_support_abort

Fixed a bug that vm_ok.sh does not detect 'aborted' status
fixed unsuccessful handshake by making err null in json response; no authentication or version check though
added more info/context in logging
Merge pull request #13 from racker/songgao/make_err_nil_when_success

fixed unsuccessful handshake by making err null in json response; no aut...
Merge pull request #12 from racker/songgao/more_info_in_logging

added more info/context in logging
supporting PROXY line at the begining of stream; guessing json before processing.