TEST: Add test for 0 blocks for UNMAP and fix num_blocks which was off by one

across the testsuite

test-tool/test_read6_simple.c

@@ -43,7 +43,7 @@ test_read6_simple(void)
 
 	logging(LOG_VERBOSE, "Test READ6 of 1-255 blocks at the end of the LUN");
 	for (i = 1; i <= 255; i++) {
-		ret = read6(iscsic, tgt_lun, num_blocks +1 - i,
+		ret = read6(iscsic, tgt_lun, num_blocks - i,
 			    i * block_size, block_size, NULL);
 		CU_ASSERT_EQUAL(ret, 0);
 	}