rewrite scripts

try to provide better syntax and avoid using bash

debian/hyperv-daemons.postinst

@@ -1,9 +1,13 @@
 #!/bin/sh
 set -e
 
-if [ "$1" = "configure" ]; then
-    if [ -d /run/systemd/system ]; then
-        if [ -z "$2" ]; then
+have_systemd=1
+[ -d /run/systemd/system ] || have_systemd=0
+
+case "$1" in
+configure )
+    if [ ${have_systemd} = 1 ] ; then
+        if [ -z "$2" ] ; then
             # On initial install make sure udev notifies systemd
             udevadm trigger || true
         else
@@ -11,7 +15,10 @@ if [ "$1" = "configure" ]; then
             systemctl try-restart hv-kvp-daemon.service hv-vss-daemon.service
         fi
     fi
-fi
+;;
+esac
+
+unset have_systemd
 
 #DEBHELPER#