systemd.bbclass: Make systemd_postinst run as intended

After the switch from using a systemctl written in Python to using the
official version of systemctl from the systemd project, the
systemd_postinst function has effectively not been executed during the
rootfs creation. The reason is that systemctl provided by
systemctl-native fails if run without arguments (as systemd_postinst
does):

  Failed to connect to system scope bus via local transport: Operation
  not permitted (consider using --machine=<user>@.host --user to connect
  to bus of other user)

This is not seen in the logs since stderr is sent to /dev/null, and the
only way to tell that there is a problem is because systemd services
that are expected to be enabled aren't running.

The reason this has gone unnoticed is because systemd_handle_machine_id
in rootfs-postcommands.bbclass will call systemctl preset-all, which in
most cases will create the missing links to enable the systemd services.

This change effectively reverts commit
a52e66762c0c51918b1ba3d4622759637b6e920a (systemd.bbclass: update
command to check systemctl available) and instead only runs systemctl
without arguments (to determine that it can communicate with systemd)
when executed on target.

(From OE-Core rev: 6cb4239b412dc782f66728e47753c1a82cccf759)

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/classes-recipe/systemd.bbclass

@@ -29,7 +29,7 @@ python __anonymous() {
 }
 
 systemd_postinst() {
-if systemctl >/dev/null 2>/dev/null; then
+if type systemctl >/dev/null 2>/dev/null; then
 	OPTS=""
 
 	if [ -n "$D" ]; then
@@ -46,7 +46,7 @@ if systemctl >/dev/null 2>/dev/null; then
 		done
 	fi
 
-	if [ -z "$D" ]; then
+	if [ -z "$D" ] && systemctl >/dev/null 2>/dev/null; then
 		# Reload only system service manager
 		# --global for daemon-reload is not supported: https://github.com/systemd/systemd/issues/19284
 		systemctl daemon-reload
@@ -66,8 +66,8 @@ fi
 }
 
 systemd_prerm() {
-if systemctl >/dev/null 2>/dev/null; then
-	if [ -z "$D" ]; then
+if type systemctl >/dev/null 2>/dev/null; then
+	if [ -z "$D" ] && systemctl >/dev/null 2>/dev/null; then
 		if [ -n "${@systemd_filter_services("${SYSTEMD_SERVICE_ESCAPED}", False, d)}" ]; then
 			systemctl stop ${@systemd_filter_services("${SYSTEMD_SERVICE_ESCAPED}", False, d)}
 			systemctl disable ${@systemd_filter_services("${SYSTEMD_SERVICE_ESCAPED}", False, d)}