Eliminate few bashisms

Using == as test condition is bashism. While ash is willing to swallow
that, there are shells that aren't.

mail_notifier/create_notification

@@ -25,8 +25,8 @@ if [ $# -ne 3 ]; then
 	exit 1
 fi
 
-if [ $1 == "-s" ]; then
-	if [ $2 == "restart" ] || [ $2 == "error" ] || [ $2 == "update" ] || [ $2 == "news" ]; then
+if [ $1 = "-s" ]; then
+	if [ $2 = "restart" ] || [ $2 = "error" ] || [ $2 = "update" ] || [ $2 = "news" ]; then
 		severity=$2
 	else
 		usage