Revert "kdump-lib.sh: Remove is_atomic"
    
    Resolves: bz1974638
    Upstream: Fedora
    Conflict: None
    
    commit 017903c3c4a69e2c4705943bbc1ae10bfb56073f
    Author: Kairui Song <kasong@redhat.com>
    Date:   Fri Jun 25 03:42:19 2021 +0800
    
        Revert "kdump-lib.sh: Remove is_atomic"
    
        Now we need this helper again, for `reset-crashkernel`
    
        This reverts commit ff46cfb19e9bf944a114164e33203b1a532d35f6.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Baoquan He <bhe@redhat.com>
    
    Signed-off-by: Kairui Song <kasong@redhat.com>