UPR: couch_upr:sasl_auth should have better error handling

Today if couch_upr:sasl_auth will crash if socket closed when sending gen_tcp:send() for authentication, which crashed called function and client process.

Probably we should have better way to handle such situation. Complete logs attached.

[error_logger:error,2014-02-14T10:53:21.899,n_0@127.0.0.1:error_logger<0.6.0>:ale_error_logger_handler:log_report:72]
=========================CRASH REPORT=========================
crasher:
initial call: xdc_upr_server:init/1
pid: <0.1064.0>
registered_name: []
exception exit: case_clause,{error,closed,
[{couch_upr,sasl_auth,4,
[

{file,"src/couch_upr.erl"}

,

{line,140}

]},
{xdc_upr_server,handle_call,3,
[

{file,"src/xdc_upr_server.erl"}

,

{line,176}

]},
{gen_server,handle_msg,5,
[

{file,"gen_server.erl"}

,

{line,585}

]},
{proc_lib,init_p_do_apply,3,
[

{file,"proc_lib.erl"}

,

{line,239}

]}]}
in function gen_server:terminate/6 (gen_server.erl, line 744)
ancestors: [<0.1020.0>,<0.1018.0>,<0.1013.0>,xdc_replication_sup,
ns_server_sup,ns_server_cluster_sup,<0.59.0>]
messages: []
links: <0.1020.0>,#Port<0.11140>
dictionary: []
trap_exit: false
status: running
heap_size: 4185
stack_size: 27
reductions: 5721
neighbours:

[error_logger:error,2014-02-14T10:53:21.912,n_0@127.0.0.1:error_logger<0.6.0>:ale_error_logger_handler:log_msg:76]** Generic server <0.1020.0> terminating

• • Last message in was start_replication
  • When Server state == [{data,
    [{"State",
    {rep_state,
    {rep,
    <<"89310cdb8f94ea7852bfae91e8c8c940/default/default">>,
    <<"default">>,
    <<"/remoteClusters/89310cdb8f94ea7852bfae91e8c8c940/buckets/default">>,
    "xmem",
    [ {optimistic_replication_threshold,256}

    ,
    

    {worker_batch_size,500}

    ,
    

    {failure_restart_interval,30}

    ,
    

    {doc_batch_size_kb,2048}

    ,
    

    {checkpoint_interval,1800}

    ,
    

    {max_concurrent_reps,4}

    ,