tests/qtest/vhost-user-blk-test: don't abort all qtests on missing envar

This test requires environment variable QTEST_QEMU_STORAGE_DAEMON_BINARY
to be defined for running. If not, it would immediately abort all qtests
and prevent other, unrelated tests from running.

To fix that, just skip vhost-user-blk-test instead and log a message
about missing environment variable.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <E1oybRD-0005D5-5r@lizzy.crudebyte.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/vhost-user-blk-test.c

@@ -983,6 +983,12 @@ static void register_vhost_user_blk_test(void)
         .before = vhost_user_blk_test_setup,
     };
 
+    if (!getenv("QTEST_QEMU_STORAGE_DAEMON_BINARY")) {
+        g_test_message("QTEST_QEMU_STORAGE_DAEMON_BINARY not defined, "
+                       "skipping vhost-user-blk-test");
+        return;
+    }
+
     /*
      * tests for vhost-user-blk and vhost-user-blk-pci
      * The tests are borrowed from tests/virtio-blk-test.c. But some tests