ci: add basic integration test for pmb

Yes, I know this is crude/basic, but others are welcome to improve it later. I think we need some integration testing asap, and this is better than nothing :D

.ci/integration.sh

+#!/bin/sh -e
+
+set -x
+
+if [ "$(id -u)" = 0 ]; then
+	exec su "${TESTUSER:-build}" -c "sh -e $0"
+fi
+
+pmaports="$(cd "$(dirname "$0")"/..; pwd -P)"
+# Make sure that the work folder format is up to date, and that there are no
+# mounts from aborted test cases (pmbootstrap#1595)
+pmbootstrap work_migrate
+pmbootstrap config aports "$pmaports"
+pmbootstrap -q shutdown
+
+# TODO: make device configurable?
+device="qemu-amd64"
+# TODO: make UI configurable?
+ui="phosh"
+pmbootstrap config device "$device"
+pmbootstrap config ui "$ui"
+
+echo "Building $ui image for $device"
+pmbootstrap -y install --zap --password 147147
+
+echo "Building $ui image for $device, with FDE"
+pmbootstrap -y install --zap --password 147147 --fde