kdump-tools uses ucf for config file management and naively
modifying the config file meant for the target system directly
will cause the file hash to not get updated in the ucf database.
This will then cause later modifications to fail because
"there's nothing to do". Although actually doing the modification
to the ucf database is messy. Let's just modify the file in the live
layer to get the behavior we want there.
We install the kdump-tools package to minimal layer via inclusion in the
server-minimal seed, but it is enabled by default. Include a new chroot
hook to set USE_KDUMP=0 to make sure it's disabled by default and let
the installer decide to enable it or not.