test-tool: use CHECK_FOR_ISCSI() helper macro

This removes a large amount of boilerplate code.

Signed-off-by: David Disseldorp <ddiss@suse.de>

test-tool/test_writeverify10_residuals.c

@@ -42,14 +42,7 @@ test_writeverify10_residuals(void)
 
         CHECK_FOR_DATALOSS;
         CHECK_FOR_SBC;
-
-        if (sd->iscsi_ctx == NULL) {
-                const char *err = "[SKIPPED] This WRITEVERIFY10 test is only "
-                        "supported for iSCSI backends";
-                logging(LOG_NORMAL, "%s", err);
-                CU_PASS(err);
-                return;
-        }
+        CHECK_FOR_ISCSI(sd);
 
         /* check if writeverify10 is supported */
         WRITEVERIFY10(sd, 0, 0, block_size, 0, 0, 0, 0, NULL,