Add logging when recieved {error, disconnected} to diagnose the cause

This commit adds logging the result of `riakc_pb_socket:is_connected/1`
when Riak CS recieved {error, disconnected} from Riak. This forms a
part of long campaign of connection problem between Riak and Riak CS.
`riakc_pb_socket:is_connected/1` returns `{false, []}` mostly when
TCP connection was closed by Riak - or by Operating System. Sometimes
increasing `somaxconn` or `pb_backlog` helps. If the second element
of the return value, the list of reasons when connecting to Riak
(technically, return value of `gen_tcp:connect` might help diagnosing
the root cause, which is usually outside Riak and Riak CS.

Those logging lines are added to major places where disconneced error
was observed. `riakc_pb_socket` could return disconneced at any call,
potentially, but these logging lines will cover most of them.

[added] This pull request also includes adding switches to change riakc
reconnect and queuing strategy, choosing `queue_if_disconnected` and
`auto_reconnect`, to do trial and errors to know CS's behaviour. The
default behaviour isn't changed.

RIAK-1242
Testing `auto_reconnect=false` and timeout.
Log (line breaks inserted):

```
00:33:05.310 [warning] Access archiver stopping with work left to do; logs will be dropped
00:33:05.310 [error] gen_server <0.417.0> terminated with reason: disconnected
00:33:05.310 [error] CRASH REPORT Process <0.417.0> with 0 neighbours exited
  with reason: disconnected in gen_server:terminate/6 line 747
00:33:05.310 [error] Supervisor {<0.290.0>,poolboy_sup} had child
   riak_cs_riakc_pool_worker started with {riak_cs_riakc_pool_worker,start_link,undefined}
   at <0.417.0> exit with reason disconnected in context child_terminated
00:33:05.314 [error] gen_fsm <0.10906.6> in state archiving terminated with reason:
   no such process or port in call to gen_server:call(<0.417.0>, is_connected, infinity)
00:33:05.314 [error] CRASH REPORT Process <0.10906.6> with 0 neighbours exited
   with reason: no such process or port in call to
   gen_server:call(<0.417.0>, is_connected, infinity) in gen_fsm:terminate/7 line 611
```

`Reason=timeout` is lost.