Add a new option for customizing version in .treeinfo
    
    There was an attempt to achieve this by customizing --version and
    --release arguments for Lorax, but Pungi does not take the [general] and
    [release] sections from its .treeinfo. Instead it was always using
    release version.
    
    The value from this new option will be put into .treeinfo and used for
    --version and --release arguments in Lorax (unless explicitly defined in
    lorax_options to another value).
    
    JIRA: COMPOSE-4029
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>