MFC r271527: MFV r271511:

Use fnvlist_* to make code more readable.

Illumos issue:
    5135 zpool_find_import_cached() can use fnvlist_*

Approved by:	re (gjb)
MFC r271528: MFV r271512:

Illumos issue:
    5136 fix write throttle comment in dsl_pool.c

Approved by:	re (gjb)
Update stable/10 to -RC1 in preparation of branching releng/10.1

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
Bump __FreeBSD_version after releng/10.1 branch.

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
Merge remote-tracking branch 'freebsd/stable/10' into hardened/10/aslr