tcmu: make cmd timeout configurable

tcmu: make cmd timeout configurable

A single daemon could implement multiple types of devices
using multuple types of real devices that may not support
restarting from crashes and/or handling tcmu timeouts. This
makes the cmd timeout configurable, so handlers that do not
support it can turn if off for now.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Orabug: 25395066
(cherry picked from commit af980e46a26ac8805685bb70c8572dbc47abb126)
Signed-off-by: Kyle Fortin <kyle.fortin@oracle.com>
Reviewed-by: Shan Hai <shan.hai@oracle.com>