enclosure rewrite on CORE

Enclosure management code doesn't scale very well on large systems (100's of HDD's). There is a ton of lock contention on "busy" systems because we subprocess for each enclosure that's detected on the system.

Furthermore, the output that is generated from subprocess is quite a bit so parsing stdout fo the child process becomes a bottleneck.

This is, arguably, one of the most critical portions of our API for enclosure management, sync'inc disks to slots to devices in the zpool etc, etc. It should be as fast as possible.

See commit with all the fixes that were committed as a work-around for U5.1 hot-fix release.
https://github.com/truenas/middleware/commit/6c639bd48a2c080be016e918421b11f41b032dae