Port following change from loader.conf to grub:

   commit db9443d131f61322b8c6bbfad92d9890cbed36bd
   Author: Craig Rodrigues <rodrigc@ixsystems.com>
   Date:   Wed Aug 28 23:01:40 2013 -0700

       Add a delay during mounting of the root file system,
       because mounting off of an IPMI virtual CD-ROM device can
       be slow.

The delay only happens if the CD-ROM device is not visible
to the kernel on bootup.  This happens sometimes when booting
off of IPMI CD-ROM devices which can be slow.