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>