Early MFC of portions of r243752 adding an auditdistd user to stable/8

Early MFC of portions of r243752 adding an auditdistd user to stable/8
in order to ease future upgrades; the remainder of r243752 is left for
a future MFC of the OpenBSM upgrade:

  Merge a number of changes required to hook up OpenBSM 1.2-alpha2's
  auditdistd (distributed audit daemon) to the build:

  - Manual cross references
  - Makefile for auditdistd
  - rc.d script, rc.conf entrie
  - New group and user for auditdistd; associated aliases, etc.

  The audit trail distribution daemon provides reliable,
  cryptographically protected (and sandboxed) delivery of audit tails
  from live clients to audit server hosts in order to both allow
  centralised analysis, and improve resilience in the event of client
  compromises: clients are not permitted to change trail contents
  after submission.

  Submitted by:   pjd
  Sponsored by:   The FreeBSD Foundation (auditdistd)

git-svn-id: svn://svn.freebsd.org/base/stable/9@243947 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f