FreeNAS Code

Restructure 4K disk handling:

- Only taste disk for 4k when we don't know we are going to do 4k disks.
Also, taste only the first disk rather than all disks;
- Remove _init_zfs_disk which is bitrot and not unused.

- Extract common code for ZFS vdev manipulation into one __prepare_zfs_vdev
and eliminate the duplicated code;
- aclmode=passthrough and aclinherit=passthrough should be set at creation
time rather than after creation;
- reload_disk() only at last.

Split the partitioning into another sequence so no cache invalidation is
needed for every disk but only once after we finished everything.

- Only restart smartd when needed.
- Fix notifier in a different way. Creating gpt partition changes
the topology so we need to invalidate cache there.

make the disk replacement works if there is more than one disk unavail

Try to cache confxml but not too aggressively.

half-way solution for zfs disk replacement

introduce a Pool object while keeping the legacy API for now

middleware method to parse a given pool name

Don't do down-then-up cycle when starting if IPv6 is already
enabled.