resolvconf: check if running systemd in postinst

Check if running systemd in postinst by testing for existence of /sys/fs/cgroup/systemd instead of checking if systemd-tmpfiles exists in PATH. This is so populate-volatile.sh update is called instead of systemd-tmpfiles --create if the system has systemd-tmpfiles installed but was booted using sysvinit.

---
 meta/recipes-connectivity/resolvconf/resolvconf_1.73.bb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index ea5b6dd..c8f510b 100644
@@ -44,7 +44,7 @@ do_install () {
 
 pkg_postinst_${PN} () {
 	if [ -z "$D" ]; then
-		if command -v systemd-tmpfiles >/dev/null; then
+		if [ -e /sys/fs/cgroup/systemd ]; then
 			systemd-tmpfiles --create
 		elif [ -e ${sysconfdir}/init.d/populate-volatile.sh ]; then
 			${sysconfdir}/init.d/populate-volatile.sh update

1.8.3.2

So this says to me that having two ways of creating files in volatile locations is stupid. Should we just split out populate-volatiles from initscripts into it's own package so it can be used by pure systemd images, and split out systemd-tmpfiles so it isn't enabled by default?
This patch solves the issue for resolvconf but there are plenty of
other recipes that don't install files/postinst for both populate-volatile and systemd-tmpfiles.

Ross