Specify the squashfs-only in the lorax_options
This will reduce both the BOOT.iso and the DVD medium size
This modification relates to the following change proposal:
https://fedoraproject.org/wiki/Category:Changes/OptimizeSquashFS
The new option should work for Pungi version 4.24 and above
Jira: RHELCMP-693
Signed-off-by: Bohdan Khomutskyi <bkhomuts@redhat.com>