Allow squashfs-only and configuration_file in lorax_options
    
    The change allows for setting the parameters as described below to Lorax.
    Lorax, a program called during the buildInstall phase, creates the SquashFS
    during the buildInstall phase.
    The Squash filesystem is present both on the DVD and the BOOT.ISO.
    
    squashfs_only --- (str) passes --squashfs-only option.
    configuration_file --- (str or scm_dict) passes -c option to Lorax.
    
    The final goal of this change is to allow for optimization of
    the installation medium size.
    
    This pull request is related to the Fedora change proposal, which is available
    at this location:
    https://fedoraproject.org/wiki/Category:Changes/OptimizeSquashFS
    See the change proposal for more information about the benefits of higher
    compression ratio.
    
    Jira: RHELCMP-693
    Signed-off-by: Bohdan Khomutskyi <bkhomuts@redhat.com>