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>

fedora.conf

@@ -105,11 +105,13 @@ buildinstall_skip = [
 lorax_options = [
   ('^.*$', {
      'x86_64': {
-         'nomacboot': False
+         'nomacboot': False,
+         'squashfs_only': True
      },
      '*': {
          'noupgrade': True,
-         'rootfs_size': 3
+         'rootfs_size': 3,
+         'squashfs_only': True
      }
   })
 ]