Always select the card before we do the 4.x specific stuff and
deselect it after setting the block size. This is a similar bug that
was fixed elsewhere, but not here. This makes sure that we leave the
card deselected at the end of the loop, and we don't send any commands
to the card without it selected.

Reviewed by: ian@
Always sync the global ZFS config cache to reflect the new mosconfig

This fixes out of date zpool.cache for root pools, which can cause issues
such as confusion of zdb etc.

MFC after:	1 month
Fix potential division by zero after r275920.

Reported by:	Coverity Scan
CID:		1260387
MFC after:	3 days
Fix build with recent binutils

Recent binutils considered the .gnu.warning.symbol section as a fatal error when
run with --fatal-warnings which makes any users of "insecure" functions from
libc failing to build with recent binutils.

Introduce a new macro: LD_FATAL_WARNINGS=no to run ld(1) with
--no-fatal-warnings for the users of "insecure" functions

Differential Revision:	https://reviews.freebsd.org/D1320