[HEAD-353] add SDC_UPGRADE_ROOT which points to root dir of upgrade.
[HEAD-353] add SDC_UPGRADE_ROOT which points to root dir of upgrade.

numericillustration/sdc-headnode,numericillustration/sdc-headnode,joyent/sdc-headnode,joyent/sdc-headnode,kaizengarden/sdc-headnode,kaizengarden/sdc-headnode,joyent/sdc-headnode,kaizengarden/sdc-headnode,numericillustration/sdc-headnode,joyent/sdc-headnode,kaizengarden/sdc-headnode