lvconvert: add infrastructure for RaidLV reshaping support
In order to support striped raid5/6/10 LV reshaping (change
of LV type, stripesize or number of legs), this patch
introduces more local infrastructure to raid_manip.c
used by followup patches.
Change:
- add missing raid1 <-> raid5 conversions to support
linear <-> raid5 <-> raid0(_meta)/striped conversions
- rename related new takeover functions to
_takeover_from_raid1_to_raid5 and _takeover_from_raid5_to_raid1,
because a reshape to > 2 legs is only possible with
raid5 layout