Add kdump anaconda addon to anaconda-tools group
    
    Kdump need the addon in live cd so that anaconda can eanble the kdump setup
    UI during intalling phase.
    
    The kdump addon is maintained in kexec-tools as a sub-package:
    kexec-tools-anaconda-addon
    
    The package size is very small, the latest one for x86_64 is around 90k.
    
    Adding it does not mean to enable it by default, one need use inst.kdump_addon
    kernel param to enable it.  Details see Fedora bug below:
    https://bugzilla.redhat.com/show_bug.cgi?id=1176483
    https://pagure.io/fedora-kickstarts/pull-request/31
    
    Per suggestion in the comments from above pull request here add it to
    anaconda-tools package group.
    
    Tested-by: Tong Li <tonli@redhat.com>