Separate var dataset for initial Zones install

with following push to build 175 :

  changeset:   1486:8d1798b41bae
  tag:         tip
  user:        Matt Keenan <matt.keenan@oracle.com>
  date:        Thu Sep 15 17:33:45 2011 +0100

  description:
    7089945 Re-enable separate /var dataset creation for non global
            zones install in AI

  modified:
    usr/src/cmd/auto-install/auto_install.py

Creation of a separate /var dataset was enabled for Global zone installs for build 174, however because of bug:

  7087267 zones with separate /var fail to boot and attach

the creation of a /var dataset for zones initial install was disabled. As this bug has now integrated into 175, we are enabling the creation of a /var dataset on iniital zones installations.