mount a filesystem with label autoinstall at /autoinstall for live-server

This is one of the ways an autoinstall file can be provided.

live-build/ubuntu-server/hooks/032-installer-squashfs.binary

@@ -42,14 +42,22 @@ setup_mountpoint binary/boot/squashfs.dir
 # to a new VT when there is no device there (LP: #1750117).
 # It would be better to have this in ../includes.binary/overlay but
 # you can't have backslashes in filenames in bzr branches!
-DEVICE_UNIT_NAME='dev-disk-by\x2duuid-00c629d6\x2d06ab\x2d4dfd\x2db21e\x2dc3186f34105d.device'
-mkdir -p "$INSTALLER_ROOT/etc/systemd/system/$DEVICE_UNIT_NAME.d"
-cat > "$INSTALLER_ROOT/etc/systemd/system/$DEVICE_UNIT_NAME.d/override.conf" <<EOF
+ANSWERS_DEVICE_UNIT='dev-disk-by\x2duuid-00c629d6\x2d06ab\x2d4dfd\x2db21e\x2dc3186f34105d.device'
+mkdir -p "$INSTALLER_ROOT/etc/systemd/system/$ANSWERS_DEVICE_UNIT.d"
+cat > "$INSTALLER_ROOT/etc/systemd/system/$ANSWERS_DEVICE_UNIT.d/override.conf" <<EOF
 [Unit]
 JobRunningTimeoutSec=0s
 Wants=subiquity_config.mount
 EOF
 
+AUTOINSTALL_DEVICE_UNIT='dev-disk-by\x2dlabel-default.device'
+mkdir -p "$INSTALLER_ROOT/etc/systemd/system/$AUTOINSTALL_DEVICE_UNIT.d"
+cat > "$INSTALLER_ROOT/etc/systemd/system/$AUTOINSTALL_DEVICE_UNIT.d.d/override.conf" <<EOF
+[Unit]
+JobRunningTimeoutSec=0s
+Wants=subiquity_autoinstall.mount
+EOF
+
 # Prepare installer layer.
 
 # Install casper for live session magic.

live-build/ubuntu-server/includes.binary/overlay/usr/lib/systemd/system/subiquity_autoinstall.mount

@@ -0,0 +1,4 @@
+[Mount]
+What=/dev/disk/by-label/autoinstall
+Where=/autoinstall
+Type=ext4