kdumpctl: Fix the matching of plus symbol by grep's EREs
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2160676
    Upstream: Fedora rawhide
    Conflict: None
    
    commit 64d93c886f4cd1bc3008e8eb9dea7cdb8e8cc601
    Author: Pingfan Liu <piliu@redhat.com>
    Date:   Fri Jun 9 16:04:29 2023 +0800
    
        kdumpctl: Fix the matching of plus symbol by grep's EREs
    
        After introducing 64k variant kernel on aarch64, an example kernel name
        looks like "vmlinuz-5.14.0-316.el9.aarch64+64k". To match the plus
        symbol, it demands an escape charater.
    
        Signed-off-by: Pingfan Liu <piliu@redhat.com>
        Reviewed-by: Philipp Rudo <prudo@redhat.com>
        Reviewed-by: Coiby Xu <coxu@redhat.com>
    
    Signed-off-by: Pingfan Liu <piliu@redhat.com>