mkdumprd: allow using dash
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit 4b4d045b8c0a7d7bf9d09b5b29bc81885e63ed2b
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Aug 11 19:55:19 2021 +0800
    
        mkdumprd: allow using dash
    
        All non-POSIX syntax in second kernel are gone, tested on Fedora 34
        with latest dracut, dash now works fine.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>