engines/sg: Make I/O error messages more informative

engines/sg: Make I/O error messages more informative

Ensure that if an I/O error is encountered that not only the error
number but also a textual error message and the engine name are
reported. Without this patch, SG error messages look like this:

fio: pid=12803, err=5/

With this patch applied SG I/O error messages change into:

fio: pid=12803, err=5/file:engines/sg.c:290, func=fio_sgio_doio, error=Input/output error

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>