MFC r216291, r216293:

MFC r216291, r216293:

MFC r216291:
Do not print OpenSolaris hint to use (non-existing) installgrub(1) command
if creating a mirror by attaching a new vdev to a root pool.

MFC r216293:
Print message with information about updating the boot code if a new
vdev is attached to a root pool (e.g. when creating a mirrored boot pool).

Reported by:	James R. Van Artsdalen (on freebsd-fs@freebsd.org)
Reviewed by:	pjd
Approved by:	re (kib), delphij (mentor)

git-svn-id: svn://svn.freebsd.org/base/stable/8@216386 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f