kdump-logger.sh: make it POSIX compatible
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit 8cd57e5565142553b1fe739afe90723359b18498
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Aug 11 19:19:59 2021 +0800
    
        kdump-logger.sh: make it POSIX compatible
    
        Refactor to remove some bash only syntax.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>