armbian-next: split prepare_host(), fix .tmp reset trap

- `prepare_host()`: split; do checks earlier and allow them to be interactive
- introduce `exit_if_countdown_not_aborted()` for "Low Disk Space" and other critical conditions
- split `prepare_host()` into interactive & non-interactive parts
- split off `clean_deprecated_mountpoints()` from prepare into `cleaning.sh`
- introduce and use `reset_uid_owner_non_recursive()` for `.tmp` reset in trap, to avoid disasters
- add more logging sections to default-build.sh, avoid unlogged parts

lib/functions/logging/traps.sh

@@ -165,3 +165,35 @@ function exit_with_error() {
 
 	exit 43
 }
+
+# This exits, unless user presses ENTER. If not interactive, user will be unable to comply and the script will exit.
+function exit_if_countdown_not_aborted() {
+	# parse
+	declare -i loops="${1}"
+	declare reason="${2}"
+	# validate
+	[[ -z "${loops}" ]] && exit_with_error "countdown_to_exit_or_just_exit_if_noninteractive() called without a number of loops"
+	[[ -z "${reason}" ]] && exit_with_error "countdown_to_exit_or_just_exit_if_noninteractive() called without a reason"
+
+	# If not interactive, just exit.
+	if [[ ! -t 1 ]]; then
+		exit_with_error "Exiting due to '${reason}' - not interactive, exiting immediately."
+	fi
+
+	display_alert "Problem detected" "${reason}" "err"
+	display_alert "Exiting in ${loops} seconds" "Press \e[0;33m<Ctrl-C>\x1B[0m to abort, \e[0;33m<Enter>\x1B[0m to ignore and continue" "err"
+	echo -n "Counting down: "
+	for i in $(seq 1 "${loops}"); do
+		declare stop_waiting=0
+		declare keep_waiting=0
+		timeout --foreground 1 bash -c "read -n1; echo \$REPLY" && stop_waiting=1 || keep_waiting=1
+		if [[ "$stop_waiting" == "1" ]]; then
+			display_alert "User pressed ENTER, continuing, albeit" "${reason}" "wrn"
+			return 0
+		fi
+		echo -n "$i... " >&2
+	done
+
+	# Countdown finished, exit.
+	exit_with_error "Exiting due to '${reason}'"
+}