Support storing image encryption keys in Vault

src/test/mock/vault.cpp

@@ -0,0 +1,17 @@
+// Copyright (c) Vitaliy Filippov, 2019+
+// License: VNPL-1.1 or GNU GPL-2.0+ (see README.md for details)
+
+#include "cluster_client.h"
+
+void cluster_client_t::vault_destroy()
+{
+}
+
+void cluster_client_t::vault_load_keys()
+{
+    if (vault_loading || !vault_key_load_queue.size())
+    {
+        return;
+    }
+    vault_loading = true;
+}