illumos gate

we are defining commands by export <CMD>=<CMD_PATH> in file zfs-tests/include/commands.cfg, but sometime on different environments we need redefine CMD

i'd like propose to use new scheme where we can redefine components on distribution if needed.
also, we need default.run file for another distributions.

example for redefined CMDs on DilOS in script:

root@dilos-zfs:/opt# cat zt.sh 
#!/bin/bash

export SUDO=/usr/bin/sudo
export CHMOD=/system/bin/chmod
export CHOWN=/system/bin/chown
export CHGRP=/system/bin/chgrp
export CP=/system/bin/cp
export DF=/system/bin/df
export PAX=/system/bin/pax
export CPIO=/system/bin/cpio
export DD=/system/bin/dd
export TAR=/system/bin/tar
export ECHO=/system/bin/echo
export PYTHON=/usr/bin/amd64/python2.7

ARGS="$*" 

if [ "x$ARGS" = "x" ]; then
        ARGS="-c /opt/dilos.run" 
fi

export DISKS="c4t0d0 c3t0d0 c2t0d0" 
export KEEP="rpool fakeroot" 
export FAKEROOT="/fakeroot/tmp" 

LOG=$(date +'%Y%m%d-%H%M')

time /opt/zfs-tests/bin/zfstest $ARGS 2>&1 | tee /var/tmp/${LOG}.zt.log.txt