install script improvements: using getent group

debian/damaris-modules.postinst

@@ -1 +1,8 @@
-addgroup --system nmr
+#!/bin/sh
+set -e
+
+if getent group nmr; then
+	echo "group nmr exists alread, doing nothing"
+else
+	addgroup --system nmr
+fi

debian/damaris-modules/etc/init.d/damaris-modules

@@ -1,10 +1,8 @@
 #!/bin/sh
 ### BEGIN INIT INFO
 # Provides:          damaris-backends
-# Required-Start:    $syslog $local_fs
-# Required-Stop:     $syslog $local_fs
-# Should-Start:      $syslog 
-# Should-Stop:       $syslog
+# Required-Start:    $syslog $remote_fs
+# Required-Stop:     $syslog $remote_fs
 # Default-Start:     2 3 4 5
 # Default-Stop:      0 1 6
 # Short-Description: Startup script to load nmr hardware drivers for use with damaris backends