Packaging Deb: configure start-stop-daemon to not go into background (#21343)

On ubuntu 14.04, which uses upstart, where as our debian package uses
sysvinit, there is no stdout/stderr message printed when starting up,
because the start-stop-daemon swallows it.

As Elasticsearch is started to daemonize, we can remove the background
flag from the start-stop-daemon and thus see, if the system does not have
enough memory for starting up - something that happens often on VMs, since
Elasticsearch 5.0 uses 2gb by default instead of one.

Relates #21300
Relates #12716

distribution/deb/src/main/packaging/init.d/elasticsearch

@@ -137,7 +137,7 @@ case "$1" in
 	fi
 
 	# Start Daemon
-	start-stop-daemon -d $ES_HOME --start -b --user "$ES_USER" -c "$ES_USER" --pidfile "$PID_FILE" --exec $DAEMON -- $DAEMON_OPTS
+	start-stop-daemon -d $ES_HOME --start --user "$ES_USER" -c "$ES_USER" --pidfile "$PID_FILE" --exec $DAEMON -- $DAEMON_OPTS
 	return=$?
 	if [ $return -eq 0 ]; then
 		i=0