MFC r227272:

MFC r227272:
  Add reference to gpart(8).

MFC r227280:
  Initialize "acc" value inside the loop to reset failed attempts.

  PR:           misc/162262

MFC r227292:
  Improve error reporting when MBR can not be written.
  Remove obsolete code which uses DIOCSMBR ioctl.
  When writing MBR first check that GEOM_MBR is available, if it is not
  available, then try write MBR directly to provider. If both are failed,
  then recommend to use gpart(8).

MFC r227295:
  Fix multi-line comment formatting.

  Pointed by:   jh

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/9@227560 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f