feat(hack): add scripts to drive the dev environment headless

Start QEMU in the background with a QMP socket and console logs, take
screenshots, press keys and wait for serial output, so the graphical boot
menu can be driven without a terminal or a window. boot.sh gets opt-in
knobs for this and behaves as before otherwise.

hack/dev/run/smoke.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+# Boots the graphical menu, moves the selection up and down, boots Linux and waits for its shell prompt.
+# Usage: smoke.sh [arch]
+# Screenshots land in target/run/<arch>/shots. The exit code is the result.
+# Environment: SMOKE_MENU_DELAY is seconds to let the menu draw (default 10), SMOKE_BOOT_TIMEOUT is
+# seconds to wait for the shell (default 180). The start.sh variables apply too.
+set -e
+
+cd "$(dirname "${0}")/../../.." || exit 1
+
+[ -n "${1}" ] && TARGET_ARCH="${1}"
+. "hack/dev/run/lib.sh"
+export TARGET_ARCH
+
+trap './hack/dev/run/stop.sh' EXIT
+
+./hack/dev/run/start.sh "${TARGET_ARCH}"
+sleep "${SMOKE_MENU_DELAY:-10}"
+
+echo "menu: $(./hack/dev/run/screenshot.sh "${SHOT_DIR}/menu.png")"
+# The default entry is the last one, so up is the key that visibly moves the selection.
+./hack/dev/run/key.sh up
+echo "up: $(./hack/dev/run/screenshot.sh "${SHOT_DIR}/menu-up.png")"
+./hack/dev/run/key.sh down ret
+
+./hack/dev/run/wait-serial.sh 'sprout:.*# ' "${SMOKE_BOOT_TIMEOUT:-180}"
+echo "ok: reached a shell on ${TARGET_ARCH}"