3641 want a histogram of compressed block sizes
Reviewed by: George Wilson <gwilson@zfsmail.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Approved by: Eric Schrock <eric.schrock@delphix.com>
3639 zpool.cache should skip over readonly pools
3640 want automatic devid updates
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Basil Crow <basil.crow@delphix.com>
Approved by: Gordon Ross <gwr@nexenta.com>
	[illumos-gate merge]

commit fb02ae025247e3b662600e5a9c1b4c33ecab7d72
    3639 zpool.cache should skip over readonly pools
    3640 want automatic devid updates
commit 490d05b9daa0e60fbb3aac647c556408e88228bd
    3641 want a histogram of compressed block sizes