[bug] errors about "attach api"

[YaoZengzeng]

(1) First, run a container with command "hypercli run -di busybox cat". Then request "POST", "/containers/"+cid+"/attach?stream=1&stdin=1&stdout=1", and read from stdout which should success, but timeout. (2) Run a container with command "hypercli run -di busybox /bin/sh -c cat >&2" Then request "POST", "/containers/"+cid+"/attach?stream=1&stdin=1&stderr=1" , and read from stderr which should success,but timeout Request "POST", "/containers/"+cid+"/attach?stream=1&stdin=1&stdout=1",and read from stderr which should timeout, but err is nil (3)Run a container with command "hypercli run -dit busybox /bin/sh -c cat >&2" Then request "POST", "/containers/"+cid+"/attach?stream=1&stdin=1&stdout=1", and read from stdout which should success but timeout