examples: additional options to iscsi-dd

this adds progress output, 16 byte CDB support, additional checks and user
settable max_in_flight and blocks_per_io.

Signed-off-by: Peter Lieven <pl@kamp.de>
examples: iscsi-dd add option to ignore errors

Signed-off-by: Peter Lieven <pl@kamp.de>
Merge pull request #118 from plieven/for-ronnie

examples: additional options to iscsi-dd