ceph-volume: skip internal raid mirror LVs in inventory

ceph-volume: skip internal raid mirror LVs in inventory

ceph-volume inventory started including all LVM mapper devices after
c06bee965f1. On hosts with raid mirrored system volumes, that pulls in
hidden legs like var_rmeta_0 which have no /dev/vg/lv node and makes
cephadm's ceph-volume inventory call fail.

Skip those internal LVs in get_devices() and avoid rewriting the device
path to a missing lv_path in Device._parse().

Fixces: https://tracker.ceph.com/issues/77486

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>