Distinguish command timeout from outqueue or waitqueue. For example,
A command sequence: ...NOP,READ,WRITE...
NOP OUT command has no dependence on backend media, it is expected to
response soon. Once NOP timeout in libiscsi:
a, the command is already sent to target, the target side does *not*
response.
b, the command is still pending in libiscsi.
Separate the two cases for trouble shooting.
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>