mkdumprd: use kdump_get_conf_val to read config values
    
    upstream: fedora
    resolves: bz2003832
    conflict: none
    
    commit 075e62252ec13e582e8aaa43a0fefee1ad5d8a58
    Author: Kairui Song <kasong@redhat.com>
    Date:   Wed Aug 4 01:58:04 2021 +0800
    
        mkdumprd: use kdump_get_conf_val to read config values
    
        Simplify the code and cover more corner cases.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Philipp Rudo <prudo@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>