Merge r229085 from head:

Merge r229085 from head:

  Default to not performing the early-boot memory tests when we detect we
  are booting inside a VM.  There are three reasons to disable this:

  o  It causes the VM host to believe that all the tested pages or RAM are
     in use.  This in turn may force the host to page out pages of RAM
     belonging to other VMs, or otherwise cause problems with fair resource
     sharing on the VM cluster.
  o  It adds significant time to the boot process (around 1 second/Gig in
     testing)
  o  It is unnecessary - the host should have already verified that the
     memory is functional etc.

  Note that this simply changes the default when in a VM - it can still be
  overridden using the hw.memtest.tests tunable.

Early MFC requested by: bz

git-svn-id: svn://svn.freebsd.org/base/stable/8@230472 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f