Skip reading /etc/defaut/grub for s390x
    
    Resolves: bz2133129
    Upstream: Fedora
    Conflict: None
    
    commit fdad7d9869a9637e6799cce222d386aed0b8781e
    Author: Coiby Xu <coxu@redhat.com>
    Date:   Thu Sep 29 12:35:00 2022 +0800
    
        Skip reading /etc/defaut/grub for s390x
    
        Currently, updating kexec-tools on s390x gives the warning
        sed: can't read /etc/default/grub: No such file or directory
    
        This happens because s390x doesn't use GRUB and /etc/default/grub
        doesn't exist. We need to skip both reading and writing to
        /etc/default/grub.
    
        Reported-by: Jie Li <jieli@redhat.com>
        Reviewed-by: Philipp Rudo <prudo@redhat.com>
        Signed-off-by: Coiby Xu <coxu@redhat.com>
    
    Signed-off-by: Coiby Xu <coxu@redhat.com>