rhevh6-post.ks: only includes virt-who for rhevh

ovirt-node uses rhevh6-post.ks as base to build the iso image.
As virt-who is only used in rhevh distro we shouldn't ship it for
non rhevh images.

Change-Id: I4dd2ff87bd7242572cddc2a83da10b0070bb27f4
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>