Use a customized emergency shell
    
    Resolves: bz1901024
    Upstream: Fedora
    Conflict: None
    
    commit 41980f30d9f5806a2e34e30fe279167c12d0ae75
    Author: Kairui Song <kasong@redhat.com>
    Date:   Mon Apr 26 17:09:57 2021 +0800
    
        Use a customized emergency shell
    
        Use a modified and minimized version of emergency shell.
        The differences of this kdump shell and dracut emergency shell are:
    
          - Kdump shell won't generate a rdsosreport automatically
          - Customized prompts
          - Never ask root password
          - Won't tangle with dracut's emergency_action. If emergency_action is
            set, dracut emergency shell will perform dracut's emergency_action
            instead of kdump final_action on exit.
          - If rd.shell=no is set, kdump shell will still work, dracut emergency
            shell won't, even if kdump failure_action is set to shell.
    
        Signed-off-by: Kairui Song <kasong@redhat.com>
        Acked-by: Coiby Xu <coxu@redhat.com>
    
    Signed-off-by: Kairui Song <kasong@redhat.com>