restorer: Use rst memory allocator for rlimits restore

Number of rlimits may vary depending on system version
criu is compiled against. So we use rst-allocator to
carry all limits read from file.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>