dracut-kdump.sh: make it POSIX compatible
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit b1339c3b8a006f95d8414c6e113fbec78bc03123
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Aug 18 21:06:52 2021 +0800
    
        dracut-kdump.sh: make it POSIX compatible
    
        POSIX doesn't support keyword `local`, so this commit reduced variable usage.
        Heredoc ("<<<") operation is also not supported, so kdump.conf is now pre-parse
        into a temp file. Also fixes many POSIX syntax errors.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>