rootfs-create: if debootstrap second stage fails, find debootstrap.log and show it so we know what the error is

- runner: let `if_error_find_files_sdcard` be a simple filename (different debootstraps put debootstrap.log in different places)

lib/functions/rootfs/rootfs-create.sh

@@ -124,6 +124,7 @@ function create_new_rootfs_cache_via_debootstrap() {
 	deploy_qemu_binary_to_chroot "${SDCARD}" # this is cleaned-up later by post_debootstrap_tweaks() @TODO: which is too late for a cache
 
 	display_alert "Installing base system" "Stage 2/2" "info"
+	declare -g -a if_error_find_files_sdcard=("debootstrap.log") # if command fails, go look for this file and show it's contents during error processing
 	declare -g if_error_detail_message="Debootstrap second stage failed ${RELEASE} ${DESKTOP_APPGROUPS_SELECTED} ${DESKTOP_ENVIRONMENT} ${BUILD_MINIMAL}"
 	chroot_sdcard LC_ALL=C LANG=C /debootstrap/debootstrap --second-stage
 	[[ ! -f "${SDCARD}/bin/bash" ]] && exit_with_error "Debootstrap first stage did not produce /bin/bash"