add scsi-target-utils pkg to support migrate.after_extensive_io.iscsi

support RHEL.5/6 Fedora
and disable legacy rhel guests as they dont have such pkg

Signed-off-by: Xiaoqing Wei <xwei@redhat.com>
Merge pull request #964 from xiaoqing-wei/add_scsi-target-utils_to_ks

add scsi-target-utils pkg to support migrate.after_extensive_io.iscsi