Write to `/var/lib/kdump` if $KDUMP_BOOTDIR not writable
    
    Resolves: bz1965952
    Upstream: Fedora
    Conflict: None
    
    commit 75bdcb7399b6fe48032a8db534e18b01206601bc
    Author: Kelvin Fan <kfan@redhat.com>
    Date:   Fri Apr 16 22:31:13 2021 +0000
    
        Write to `/var/lib/kdump` if $KDUMP_BOOTDIR not writable
    
        The `/boot` directory on some operating systems might be read-only.
        If we cannot write to `$KDUMP_BOOTDIR` when generating the kdump
        initrd, attempt to place the generated initrd at `/var/lib/kdump`
        instead.
    
        Signed-off by: Kelvin Fan <kelvinfan001@gmail.com>
        Acked-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>