Option for using systemd-nspawn instead of chroot for hooks.

Installation of flatpaks doesn't work with normal chroots.
This patch enables support for using systemd-nspawn in hooks.

Gbp-Dch: Short
Closes: #965953

debian/control

@@ -27,6 +27,7 @@ Recommends:
  live-boot-doc,
  live-config-doc,
  live-manual-html | live-manual,
+ systemd-container,
  wget,
  xz-utils,
 Suggests:

scripts/build/chroot_hooks

@@ -72,12 +72,20 @@ rmdir chroot/root/lb_chroot_hooks
 rmdir --ignore-fail-on-non-empty chroot/root
 
 ## Processing local hooks
-if ls config/hooks/normal/*.chroot config/hooks/live/*.chroot > /dev/null 2>&1
+if ls config/hooks/normal/*.chroot > /dev/null 2>&1 && (
+   ls config/hooks/live/*.chroot > /dev/null 2>&1 ||
+   ls config/hooks/live/*.container > /dev/null 2>&1 )
 then
+	# If a systemd-nspawn hook exists check if package is installed
+	if ls config/hooks/live/*.container > /dev/null 2>&1
+	then
+		Check_package host /usr/bin/systemd-nspawn systemd-container
+	fi
+
 	# Restoring cache
 	Restore_package_cache chroot
 
-	for HOOK in config/hooks/normal/*.chroot config/hooks/live/*.chroot
+	for HOOK in config/hooks/normal/*.chroot config/hooks/live/*.chroot config/hooks/live/*.container
 	do
 		if [ ! -e "${HOOK}" ]
 		then
@@ -94,7 +102,17 @@ then
 		fi
 
 		# Executing hook
+		Echo_message "Executing hook ${HOOK}..."
+		case "${HOOK}" in
+			*.container)
+				umount chroot/proc
+				systemd-nspawn --capability=all -D chroot "/root/$(basename ${HOOK})" || { Echo_error "${HOOK} failed (exit non-zero). You should check for errors."; exit 1 ;}
+				mount proc-live -t proc chroot/proc
+				;;
+			*)
 				Chroot chroot "/root/$(basename ${HOOK})" || { Echo_error "${HOOK} failed (exit non-zero). You should check for errors."; exit 1 ;}
+				;;
+		esac
 
 		# Removing hook
 		rm -f chroot/root/"$(basename ${HOOK})"