fix #3313: restore: keep unprivileged status from archive config

fix #3313: restore: keep unprivileged status from archive config

Since pct defaults to privileged containers, it restores the
container as privileged when `--unprivileged 1` is not passed.
Instead we should check the old configuration and retrieve it from
there.

This way, when one creates an unprivileged container, it will be
still be unprivileged after restore, if not overwritten by API
arguments.

Signed-off-by: Oguz Bektas <o.bektas@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>