add stream throws exception in stats_collector

Open connection and create a consumer.
Add stream to consumer fails and the bucket state changes to inactive.

[stats:error,2014-02-04T17:20:06.440,ns_1@127.0.0.1:<0.12669.1>:stats_collector:handle_info:119]Exception in stats collector: {exit,
badmatch,{error,closed,
{gen_server,call,
['ns_memcached-default',

{stats,<<>>}

,
180000]}},
[

{gen_server,call,3}

,

{ns_memcached,do_call,3}

,

{stats_collector,grab_all_stats,1}

,

{stats_collector,handle_info,2}

,

{gen_server,handle_msg,5}

,

{proc_lib,init_p_do_apply,3}

]}

[ns_server:error,2014-02-04T17:20:06.644,ns_1@127.0.0.1:ns_doctor<0.630.0>:ns_doctor:update_status:235]The following buckets became not ready on node 'ns_1@127.0.0.1': ["default"], those of them are active ["default"]