Fix dib-init-system for Debian Jessie and Debian Stretch

On Debian Jessie and Debian Stretch systemctl is in /bin.
If the package systemd-sysv is not installed the script
dib-init-system did not find the init system.
This patch fixes the problem: it also looks in /bin
for systemctl and if found decides for systemd.

Change-Id: I5a18052a070bad5e16b14672237a1e2b38513949
Signed-off-by: Andreas Florath <andreas@florath.net>

diskimage_builder/elements/dib-init-system/dib-init-system

@@ -6,7 +6,10 @@ fi
 set -eu
 set -o pipefail
 
-if [[ -f /usr/bin/systemctl ]]; then
+# Debian Jessie and Debian Stretch use /bin/systemctl.
+# (/sbin/init is only available if systemd-sysv is installed.)
+
+if [ -f /usr/bin/systemctl -o -f /bin/systemctl ]; then
     echo "systemd"
 elif [[ -f /sbin/initctl ]]; then
     echo "upstart"

releasenotes/notes/dib-init-system_fix_for_debian_jessie-c6f7261ee84dad27.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - dib-init-system did not correctly find the
+    init system for Debian Jessie and Debian Stretch.
+    This version also looks for /bin/systemctl as
+    as hint for systemd and fixes the problem.