mkdumprd: Start using --hostonly and --add kdumpbase while calling dracut
    
    BZ: 817044
    
    Harald suggested that we use --add kdumpbase instead of -m kdumpbsae. As
    -m means only use modules specified on the command line. I am not sure
    that kdump will ever know the list of modules it wants to use. It might
    be a good idea to let dracut decide it based on --mount option.
    
    Also start using --hostonly to make sure atleast our default dumping to
    root disk always works.
    
    I also noticed that with --add and --hostonly initramfs size came down. So
    for the time being just bring down the initramfs size.
    
    But it still looks big and this area will require more experimentation and
    bug fixing to make sure we are generatiing optimal size images for kdump
    purposes and get rid of bloat. I am just beginning to understand dracut,
    so expect more churn in this area down the line from me.
    
    I am posting this patch for the bz opened again F18. As it is reducing
    initramfs size significantly, I think it is a good idea to commit it
    in F17 branch also.
    
    Following is image size comparision.
    
    Dump to root disk.
    ------------------
    vanilla compressed: 13MB
    hostonly compressed: 7.5MB
    
    Dump to nfs
    -----------
    vanilla compressed: 24MB
    hostonly compressed: 13MB
    
    Dump over ssh
    -------------
    vanilla compressed: 23.5 MB
    hostonly compressed: 12 MB
    
    Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
    Acked-by: Dave Young <dyoung@redhat.com>