tests: fix -Werror=maybe-uninitialized false-positive

../tests/unit/test-block-iothread.c:773:17: error: ‘job’ may be used uninitialized [-Werror=maybe-uninitialized]
/usr/include/glib-2.0/glib/gtestutils.h:73:53: error: ‘ret’ may be used uninitialized [-Werror=maybe-uninitialized]

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

tests/unit/test-bdrv-drain.c

@@ -722,7 +722,7 @@ static void test_blockjob_common_drain_node(enum drain_type drain_type,
     BlockJob *job;
     TestBlockJob *tjob;
     IOThread *iothread = NULL;
-    int ret;
+    int ret = -1;
 
     src = bdrv_new_open_driver(&bdrv_test, "source", BDRV_O_RDWR,
                                &error_abort);

tests/unit/test-block-iothread.c

@@ -745,7 +745,7 @@ static void test_propagate_mirror(void)
     AioContext *main_ctx = qemu_get_aio_context();
     BlockDriverState *src, *target, *filter;
     BlockBackend *blk;
-    Job *job;
+    Job *job = NULL;
     Error *local_err = NULL;
 
     /* Create src and target*/