vstorage: Fix build

Needed storage_util.h - missed while merging '5f07c3c0' with
commit id '479a2f16'.
Signed-off-by: NOlga Krishtal <okrishtal@virtuozzo.com>

src/storage/storage_backend_vstorage.c

@@ -9,6 +9,7 @@
 #include <mntent.h>
 #include <pwd.h>
 #include <grp.h>
+#include "storage_util.h"
 
 #define VIR_FROM_THIS VIR_FROM_STORAGE