namespaces: don't leak memory on error paths

CID 159849 (#4 of 4): Resource leak (RESOURCE_LEAK)
15. leaked_storage: Variable jn going out of scope leaks the storage it points to.

Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>