TESTS: add a flag --usb so we can clamp all i/o to at most 120k

Add checks for maximum tranfer length to all commands that are limited
by BlockLimits/MTL

test-tool/test_verify16_0blocks.c

@@ -33,6 +33,7 @@ test_verify16_0blocks(void)
 	ret = verify16(iscsic, tgt_lun, 0, 0, block_size,
 		     0, 0, 1, NULL);
 	if (ret == -2) {
+		logging(LOG_NORMAL, "[SKIPPED] VERIFY16 is not implemented.");
 		CU_PASS("[SKIPPED] Target does not support VERIFY16. Skipping test");
 		return;
 	}